spanner

package
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 Go to latest Published: Oct 13, 2020 License: Apache-2.0 Imports: 39 Imported by: 0

Documentation

Overview

Package spanner provides a client for reading and writing to Cloud Spanner databases. See the packages under admin for clients that operate on databases and instances.

Note: This package is in beta. Some backwards-incompatible changes may occur.

See https://cloud.google.com/spanner/docs/getting-started/go/ for an introduction to Cloud Spanner and additional help on using this API.

See https://godoc.org/cloud.google.com/go for authentication, timeouts, connection pooling and similar aspects of this package.

Creating a Client

To start working with this package, create a client that refers to the database of interest: 

ctx := context.Background()
client, err := spanner.NewClient(ctx, "projects/P/instances/I/databases/D")
if err != nil {
    // TODO: Handle error.
}
defer client.Close()

Remember to close the client after use to free up the sessions in the session pool.

Simple Reads and Writes

Two Client methods, Apply and Single, work well for simple reads and writes. As a quick introduction, here we write a new row to the database and read it back: 

_, err := client.Apply(ctx, []*spanner.Mutation{
    spanner.Insert("Users",
        []string{"name", "email"},
        []interface{}{"alice", "a@example.com"})})
if err != nil {
    // TODO: Handle error.
}
row, err := client.Single().ReadRow(ctx, "Users",
    spanner.Key{"alice"}, []string{"email"})
if err != nil {
    // TODO: Handle error.
}

All the methods used above are discussed in more detail below.

Keys

Every Cloud Spanner row has a unique key, composed of one or more columns. Construct keys with a literal of type Key: 

key1 := spanner.Key{"alice"}

KeyRanges

The keys of a Cloud Spanner table are ordered. You can specify ranges of keys using the KeyRange type: 

kr1 := spanner.KeyRange{Start: key1, End: key2}

By default, a KeyRange includes its start key but not its end key. Use the Kind field to specify other boundary conditions: 

// include both keys
kr2 := spanner.KeyRange{Start: key1, End: key2, Kind: spanner.ClosedClosed}

KeySets

A KeySet represents a set of keys. A single Key or KeyRange can act as a KeySet. Use the KeySets function to build the union of several KeySets: 

ks1 := spanner.KeySets(key1, key2, kr1, kr2)

AllKeys returns a KeySet that refers to all the keys in a table: 

ks2 := spanner.AllKeys()

Transactions

All Cloud Spanner reads and writes occur inside transactions. There are two types of transactions, read-only and read-write. Read-only transactions cannot change the database, do not acquire locks, and may access either the current database state or states in the past. Read-write transactions can read the database before writing to it, and always apply to the most recent database state.

Single Reads

The simplest and fastest transaction is a ReadOnlyTransaction that supports a single read operation. Use Client.Single to create such a transaction. You can chain the call to Single with a call to a Read method.

When you only want one row whose key you know, use ReadRow. Provide the table name, key, and the columns you want to read: 

row, err := client.Single().ReadRow(ctx, "Accounts", spanner.Key{"alice"}, []string{"balance"})

Read multiple rows with the Read method. It takes a table name, KeySet, and list of columns: 

iter := client.Single().Read(ctx, "Accounts", keyset1, columns)

Read returns a RowIterator. You can call the Do method on the iterator and pass a callback: 

err := iter.Do(func(row *Row) error {
   // TODO: use row
   return nil
})

RowIterator also follows the standard pattern for the Google Cloud Client Libraries: 

defer iter.Stop()
for {
    row, err := iter.Next()
    if err == iterator.Done {
        break
    }
    if err != nil {
        // TODO: Handle error.
    }
    // TODO: use row
}

Always call Stop when you finish using an iterator this way, whether or not you iterate to the end. (Failing to call Stop could lead you to exhaust the database's session quota.)

To read rows with an index, use ReadUsingIndex.

Statements

The most general form of reading uses SQL statements. Construct a Statement with NewStatement, setting any parameters using the Statement's Params map: 

stmt := spanner.NewStatement("SELECT First, Last FROM SINGERS WHERE Last >= @start")
stmt.Params["start"] = "Dylan"

You can also construct a Statement directly with a struct literal, providing your own map of parameters.

Use the Query method to run the statement and obtain an iterator: 

iter := client.Single().Query(ctx, stmt)

Rows

Once you have a Row, via an iterator or a call to ReadRow, you can extract column values in several ways. Pass in a pointer to a Go variable of the appropriate type when you extract a value.

You can extract by column position or name: 

err := row.Column(0, &name)
err = row.ColumnByName("balance", &balance)

You can extract all the columns at once: 

err = row.Columns(&name, &balance)

Or you can define a Go struct that corresponds to your columns, and extract into that: 

var s struct { Name string; Balance int64 }
err = row.ToStruct(&s)

For Cloud Spanner columns that may contain NULL, use one of the NullXXX types, like NullString: 

var ns spanner.NullString
if err := row.Column(0, &ns); err != nil {
    // TODO: Handle error.
}
if ns.Valid {
    fmt.Println(ns.StringVal)
} else {
    fmt.Println("column is NULL")
}

Multiple Reads

To perform more than one read in a transaction, use ReadOnlyTransaction: 

txn := client.ReadOnlyTransaction()
defer txn.Close()
iter := txn.Query(ctx, stmt1)
// ...
iter =  txn.Query(ctx, stmt2)
// ...

You must call Close when you are done with the transaction.

Timestamps and Timestamp Bounds

Cloud Spanner read-only transactions conceptually perform all their reads at a single moment in time, called the transaction's read timestamp. Once a read has started, you can call ReadOnlyTransaction's Timestamp method to obtain the read timestamp.

By default, a transaction will pick the most recent time (a time where all previously committed transactions are visible) for its reads. This provides the freshest data, but may involve some delay. You can often get a quicker response if you are willing to tolerate "stale" data. You can control the read timestamp selected by a transaction by calling the WithTimestampBound method on the transaction before using it. For example, to perform a query on data that is at most one minute stale, use 

client.Single().
    WithTimestampBound(spanner.MaxStaleness(1*time.Minute)).
    Query(ctx, stmt)

See the documentation of TimestampBound for more details.

Mutations

To write values to a Cloud Spanner database, construct a Mutation. The spanner package has functions for inserting, updating and deleting rows. Except for the Delete methods, which take a Key or KeyRange, each mutation-building function comes in three varieties.

One takes lists of columns and values along with the table name: 

m1 := spanner.Insert("Users",
    []string{"name", "email"},
    []interface{}{"alice", "a@example.com"})

One takes a map from column names to values: 

m2 := spanner.InsertMap("Users", map[string]interface{}{
    "name":  "alice",
    "email": "a@example.com",
})

And the third accepts a struct value, and determines the columns from the struct field names: 

type User struct { Name, Email string }
u := User{Name: "alice", Email: "a@example.com"}
m3, err := spanner.InsertStruct("Users", u)

Writes

To apply a list of mutations to the database, use Apply: 

_, err := client.Apply(ctx, []*spanner.Mutation{m1, m2, m3})

If you need to read before writing in a single transaction, use a ReadWriteTransaction. ReadWriteTransactions may abort and need to be retried. You pass in a function to ReadWriteTransaction, and the client will handle the retries automatically. Use the transaction's BufferWrite method to buffer mutations, which will all be executed at the end of the transaction: 

_, err := client.ReadWriteTransaction(ctx, func(ctx context.Context, txn *spanner.ReadWriteTransaction) error {
    var balance int64
    row, err := txn.ReadRow(ctx, "Accounts", spanner.Key{"alice"}, []string{"balance"})
    if err != nil {
        // This function will be called again if this is an IsAborted error.
        return err
    }
    if err := row.Column(0, &balance); err != nil {
        return err
    }

    if balance <= 10 {
        return errors.New("insufficient funds in account")
    }
    balance -= 10
    m := spanner.Update("Accounts", []string{"user", "balance"}, []interface{}{"alice", balance})
    txn.BufferWrite([]*spanner.Mutation{m})

    // The buffered mutation will be committed.  If the commit
    // fails with an IsAborted error, this function will be called
    // again.
    return nil
})

DML and Partitioned DML

Spanner supports DML statements like INSERT, UPDATE and DELETE. Use ReadWriteTransaction.Update to run DML statements. It returns the number of rows affected. (You can call use ReadWriteTransaction.Query with a DML statement. The first call to Next on the resulting RowIterator will return iterator.Done, and the RowCount field of the iterator will hold the number of affected rows.)

For large databases, it may be more efficient to partition the DML statement. Use client.PartitionedUpdate to run a DML statement in this way. Not all DML statements can be partitioned.

Tracing

This client has been instrumented to use OpenCensus tracing (http://opencensus.io). To enable tracing, see "Enabling Tracing for a Program" at https://godoc.org/go.opencensus.io/trace. OpenCensus tracing requires Go 1.8 or higher.

Index

Examples

Constants

View Source 
const (
	// Scope is the scope for Cloud Spanner Data API.
	Scope = "https://www.googleapis.com/auth/spanner.data"

	// AdminScope is the scope for Cloud Spanner Admin APIs.
	AdminScope = "https://www.googleapis.com/auth/spanner.admin"
)

Variables

View Source 
var (
	// OpenSessionCount is a measure of the number of sessions currently opened.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	OpenSessionCount = stats.Int64(statsPrefix+"open_session_count", "Number of sessions currently opened",
		stats.UnitDimensionless)

	// OpenSessionCountView is a view of the last value of OpenSessionCount.
	// It is EXPERIMENTAL and subject to change or removal without notice.
	OpenSessionCountView = &view.View{
		Name:        OpenSessionCount.Name(),
		Description: OpenSessionCount.Description(),
		Measure:     OpenSessionCount,
		Aggregation: view.LastValue(),
	}
)
View Source 
var (
	// CommitTimestamp is a special value used to tell Cloud Spanner
	// to insert the commit timestamp of the transaction into a column.
	// It can be used in a Mutation, or directly used in
	// InsertStruct or InsertMap. See ExampleCommitTimestamp.
	// This is just a placeholder and the actual value stored in this
	// variable has no meaning.
	CommitTimestamp = commitTimestamp
)

Functions

func ErrCode 

func ErrCode(err error) codes.Code

ErrCode extracts the canonical error code from a Go error.

func ErrDesc 

func ErrDesc(err error) string

ErrDesc extracts the Cloud Spanner error description from a Go error.

Types

type ApplyOption 

type ApplyOption func(*applyOption)

An ApplyOption is an optional argument to Apply.

func ApplyAtLeastOnce 

func ApplyAtLeastOnce() ApplyOption

ApplyAtLeastOnce returns an ApplyOption that removes replay protection.

With this option, Apply may attempt to apply mutations more than once; if the mutations are not idempotent, this may lead to a failure being reported when the mutation was applied more than once. For example, an insert may fail with ALREADY_EXISTS even though the row did not exist before Apply was called. For this reason, most users of the library will prefer not to use this option. However, ApplyAtLeastOnce requires only a single RPC, whereas Apply's default replay protection may require an additional RPC. So this option may be appropriate for latency sensitive and/or high throughput blind writing.

type BatchReadOnlyTransaction added in v0.20.0 

type BatchReadOnlyTransaction struct {
	ReadOnlyTransaction
	ID BatchReadOnlyTransactionID
}

BatchReadOnlyTransaction is a ReadOnlyTransaction that allows for exporting arbitrarily large amounts of data from Cloud Spanner databases. BatchReadOnlyTransaction partitions a read/query request. Read/query request can then be executed independently over each partition while observing the same snapshot of the database. BatchReadOnlyTransaction can also be shared across multiple clients by passing around the BatchReadOnlyTransactionID and then recreating the transaction using Client.BatchReadOnlyTransactionFromID.

Note: if a client is used only to run partitions, you can create it using a ClientConfig with both MinOpened and MaxIdle set to zero to avoid creating unnecessary sessions. You can also avoid excess gRPC channels by setting ClientConfig.NumChannels to the number of concurrently active BatchReadOnlyTransactions you expect to have.

func (*BatchReadOnlyTransaction) AnalyzeQuery added in v0.20.0 

func (t *BatchReadOnlyTransaction) AnalyzeQuery(ctx context.Context, statement Statement) (*sppb.QueryPlan, error)

AnalyzeQuery returns the query plan for statement.

func (*BatchReadOnlyTransaction) Cleanup added in v0.20.0 

func (t *BatchReadOnlyTransaction) Cleanup(ctx context.Context)

Cleanup cleans up all the resources used by this transaction and makes it unusable. Once this method is invoked, the transaction is no longer usable anywhere, including other clients/processes with which this transaction was shared.

Calling Cleanup is optional, but recommended. If Cleanup is not called, the transaction's resources will be freed when the session expires on the backend and is deleted. For more information about recycled sessions, see https://cloud.google.com/spanner/docs/sessions.

func (*BatchReadOnlyTransaction) Close added in v0.20.0 

func (t *BatchReadOnlyTransaction) Close()

Close marks the txn as closed.

func (*BatchReadOnlyTransaction) Execute added in v0.20.0 

func (t *BatchReadOnlyTransaction) Execute(ctx context.Context, p *Partition) *RowIterator

Execute runs a single Partition obtained from PartitionRead or PartitionQuery.

func (*BatchReadOnlyTransaction) PartitionQuery added in v0.20.0 

func (t *BatchReadOnlyTransaction) PartitionQuery(ctx context.Context, statement Statement, opt PartitionOptions) ([]*Partition, error)

PartitionQuery returns a list of Partitions that can be used to execute a query against the database.

func (*BatchReadOnlyTransaction) PartitionRead added in v0.20.0 

func (t *BatchReadOnlyTransaction) PartitionRead(ctx context.Context, table string, keys KeySet, columns []string, opt PartitionOptions) ([]*Partition, error)

PartitionRead returns a list of Partitions that can be used to read rows from the database. These partitions can be executed across multiple processes, even across different machines. The partition size and count hints can be configured using PartitionOptions.

func (*BatchReadOnlyTransaction) PartitionReadUsingIndex added in v0.20.0 

func (t *BatchReadOnlyTransaction) PartitionReadUsingIndex(ctx context.Context, table, index string, keys KeySet, columns []string, opt PartitionOptions) ([]*Partition, error)

PartitionReadUsingIndex returns a list of Partitions that can be used to read rows from the database using an index.

func (*BatchReadOnlyTransaction) Query added in v0.20.0 

func (t *BatchReadOnlyTransaction) Query(ctx context.Context, statement Statement) *RowIterator

Query executes a query against the database. It returns a RowIterator for retrieving the resulting rows.

Query returns only row data, without a query plan or execution statistics. Use QueryWithStats to get rows along with the plan and statistics. Use AnalyzeQuery to get just the plan.

func (*BatchReadOnlyTransaction) QueryWithStats added in v0.20.0 

func (t *BatchReadOnlyTransaction) QueryWithStats(ctx context.Context, statement Statement) *RowIterator

Query executes a SQL statement against the database. It returns a RowIterator for retrieving the resulting rows. The RowIterator will also be populated with a query plan and execution statistics.

func (*BatchReadOnlyTransaction) Read added in v0.20.0 

func (t *BatchReadOnlyTransaction) Read(ctx context.Context, table string, keys KeySet, columns []string) *RowIterator

Read returns a RowIterator for reading multiple rows from the database.

func (*BatchReadOnlyTransaction) ReadRow added in v0.20.0 

func (t *BatchReadOnlyTransaction) ReadRow(ctx context.Context, table string, key Key, columns []string) (*Row, error)

ReadRow reads a single row from the database.

If no row is present with the given key, then ReadRow returns an error where spanner.ErrCode(err) is codes.NotFound.

func (*BatchReadOnlyTransaction) ReadUsingIndex added in v0.20.0 

func (t *BatchReadOnlyTransaction) ReadUsingIndex(ctx context.Context, table, index string, keys KeySet, columns []string) (ri *RowIterator)

ReadUsingIndex calls ReadWithOptions with ReadOptions{Index: index}.

func (*BatchReadOnlyTransaction) ReadWithOptions added in v0.20.0 

func (t *BatchReadOnlyTransaction) ReadWithOptions(ctx context.Context, table string, keys KeySet, columns []string, opts *ReadOptions) (ri *RowIterator)

ReadWithOptions returns a RowIterator for reading multiple rows from the database. Pass a ReadOptions to modify the read operation.

type BatchReadOnlyTransactionID added in v0.20.0 

type BatchReadOnlyTransactionID struct {
	// contains filtered or unexported fields
}

BatchReadOnlyTransactionID is a unique identifier for a BatchReadOnlyTransaction. It can be used to re-create a BatchReadOnlyTransaction on a different machine or process by calling Client.BatchReadOnlyTransactionFromID.

func (BatchReadOnlyTransactionID) MarshalBinary added in v0.20.0 

func (tid BatchReadOnlyTransactionID) MarshalBinary() (data []byte, err error)

MarshalBinary implements BinaryMarshaler.

func (*BatchReadOnlyTransactionID) UnmarshalBinary added in v0.20.0 

func (tid *BatchReadOnlyTransactionID) UnmarshalBinary(data []byte) error

UnmarshalBinary implements BinaryUnmarshaler.

type Client 

type Client struct {
	// contains filtered or unexported fields
}

Client is a client for reading and writing data to a Cloud Spanner database. A client is safe to use concurrently, except for its Close method.

func NewClient 

func NewClient(ctx context.Context, database string, opts ...option.ClientOption) (*Client, error)

NewClient creates a client to a database. A valid database name has the form projects/PROJECT_ID/instances/INSTANCE_ID/databases/DATABASE_ID. It uses a default configuration.

Example 
package main

import (
	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

func main() {
	ctx := context.Background()
	const myDB = "projects/my-project/instances/my-instance/database/my-db"
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	_ = client // TODO: Use client.
}

Output:

func NewClientWithConfig 

func NewClientWithConfig(ctx context.Context, database string, config ClientConfig, opts ...option.ClientOption) (c *Client, err error)

NewClientWithConfig creates a client to a database. A valid database name has the form projects/PROJECT_ID/instances/INSTANCE_ID/databases/DATABASE_ID.

Example 
package main

import (
	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

func main() {
	ctx := context.Background()
	const myDB = "projects/my-project/instances/my-instance/database/my-db"
	client, err := spanner.NewClientWithConfig(ctx, myDB, spanner.ClientConfig{
		NumChannels: 10,
	})
	if err != nil {
		// TODO: Handle error.
	}
	_ = client     // TODO: Use client.
	client.Close() // Close client when done.
}

Output:

func (*Client) Apply 

func (c *Client) Apply(ctx context.Context, ms []*Mutation, opts ...ApplyOption) (commitTimestamp time.Time, err error)

Apply applies a list of mutations atomically to the database.

Example 
package main

import (
	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	m := spanner.Update("Users", []string{"name", "email"}, []interface{}{"alice", "a@example.com"})
	_, err = client.Apply(ctx, []*spanner.Mutation{m})
	if err != nil {
		// TODO: Handle error.
	}
}

Output:

func (*Client) BatchReadOnlyTransaction added in v0.20.0 

func (c *Client) BatchReadOnlyTransaction(ctx context.Context, tb TimestampBound) (*BatchReadOnlyTransaction, error)

BatchReadOnlyTransaction returns a BatchReadOnlyTransaction that can be used for partitioned reads or queries from a snapshot of the database. This is useful in batch processing pipelines where one wants to divide the work of reading from the database across multiple machines.

Note: This transaction does not use the underlying session pool but creates a new session each time, and the session is reused across clients.

You should call Close() after the txn is no longer needed on local client, and call Cleanup() when the txn is finished for all clients, to free the session.

Example 
package main

import (
	"sync"

	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
	"google.golang.org/api/iterator"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	var (
		client *spanner.Client
		txn    *spanner.BatchReadOnlyTransaction
		err    error
	)
	if client, err = spanner.NewClient(ctx, myDB); err != nil {
		// TODO: Handle error.
	}
	defer client.Close()
	if txn, err = client.BatchReadOnlyTransaction(ctx, spanner.StrongRead()); err != nil {
		// TODO: Handle error.
	}
	defer txn.Close()

	// Singer represents the elements in a row from the Singers table.
	type Singer struct {
		SingerID   int64
		FirstName  string
		LastName   string
		SingerInfo []byte
	}
	stmt := spanner.Statement{SQL: "SELECT * FROM Singers;"}
	partitions, err := txn.PartitionQuery(ctx, stmt, spanner.PartitionOptions{})
	if err != nil {
		// TODO: Handle error.
	}
	// Note: here we use multiple goroutines, but you should use separate processes/machines.
	wg := sync.WaitGroup{}
	for i, p := range partitions {
		wg.Add(1)
		go func(i int, p *spanner.Partition) {
			defer wg.Done()
			iter := txn.Execute(ctx, p)
			defer iter.Stop()
			for {
				row, err := iter.Next()
				if err == iterator.Done {
					break
				} else if err != nil {
					// TODO: Handle error.
				}
				var s Singer
				if err := row.ToStruct(&s); err != nil {
					// TODO: Handle error.
				}
				_ = s // TODO: Process the row.
			}
		}(i, p)
	}
	wg.Wait()
}

Output:

func (*Client) BatchReadOnlyTransactionFromID added in v0.20.0 

func (c *Client) BatchReadOnlyTransactionFromID(tid BatchReadOnlyTransactionID) *BatchReadOnlyTransaction

BatchReadOnlyTransactionFromID reconstruct a BatchReadOnlyTransaction from BatchReadOnlyTransactionID

func (*Client) Close 

func (c *Client) Close()

Close closes the client.

func (*Client) PartitionedUpdate added in v0.30.0 

func (c *Client) PartitionedUpdate(ctx context.Context, statement Statement) (count int64, err error)

PartitionedUpdate executes a DML statement in parallel across the database, using separate, internal transactions that commit independently. The DML statement must be fully partitionable: it must be expressible as the union of many statements each of which accesses only a single row of the table. The statement should also be idempotent, because it may be applied more than once.

PartitionedUpdate returns an estimated count of the number of rows affected. The actual number of affected rows may be greater than the estimate.

func (*Client) ReadOnlyTransaction 

func (c *Client) ReadOnlyTransaction() *ReadOnlyTransaction

ReadOnlyTransaction returns a ReadOnlyTransaction that can be used for multiple reads from the database. You must call Close() when the ReadOnlyTransaction is no longer needed to release resources on the server.

ReadOnlyTransaction will use a strong TimestampBound by default. Use ReadOnlyTransaction.WithTimestampBound to specify a different TimestampBound. A non-strong bound can be used to reduce latency, or "time-travel" to prior versions of the database, see the documentation of TimestampBound for details.

Example 
package main

import (
	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	t := client.ReadOnlyTransaction()
	defer t.Close()
	// TODO: Read with t using Read, ReadRow, ReadUsingIndex, or Query.
}

Output:

func (*Client) ReadWriteTransaction 

func (c *Client) ReadWriteTransaction(ctx context.Context, f func(context.Context, *ReadWriteTransaction) error) (commitTimestamp time.Time, err error)

ReadWriteTransaction executes a read-write transaction, with retries as necessary.

The function f will be called one or more times. It must not maintain any state between calls.

If the transaction cannot be committed or if f returns an IsAborted error, ReadWriteTransaction will call f again. It will continue to call f until the transaction can be committed or the Context times out or is cancelled. If f returns an error other than IsAborted, ReadWriteTransaction will abort the transaction and return the error.

To limit the number of retries, set a deadline on the Context rather than using a fixed limit on the number of attempts. ReadWriteTransaction will retry as needed until that deadline is met.

Example 
package main

import (
	"errors"

	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	_, err = client.ReadWriteTransaction(ctx, func(ctx context.Context, txn *spanner.ReadWriteTransaction) error {
		var balance int64
		row, err := txn.ReadRow(ctx, "Accounts", spanner.Key{"alice"}, []string{"balance"})
		if err != nil {
			// This function will be called again if this is an
			// IsAborted error.
			return err
		}
		if err := row.Column(0, &balance); err != nil {
			return err
		}

		if balance <= 10 {
			return errors.New("insufficient funds in account")
		}
		balance -= 10
		m := spanner.Update("Accounts", []string{"user", "balance"}, []interface{}{"alice", balance})
		return txn.BufferWrite([]*spanner.Mutation{m})
		// The buffered mutation will be committed.  If the commit
		// fails with an IsAborted error, this function will be called
		// again.
	})
	if err != nil {
		// TODO: Handle error.
	}
}

Output:

func (*Client) Single 

func (c *Client) Single() *ReadOnlyTransaction

Single provides a read-only snapshot transaction optimized for the case where only a single read or query is needed. This is more efficient than using ReadOnlyTransaction() for a single read or query.

Single will use a strong TimestampBound by default. Use ReadOnlyTransaction.WithTimestampBound to specify a different TimestampBound. A non-strong bound can be used to reduce latency, or "time-travel" to prior versions of the database, see the documentation of TimestampBound for details.

Example 
package main

import (
	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	iter := client.Single().Query(ctx, spanner.NewStatement("SELECT FirstName FROM Singers"))
	_ = iter // TODO: iterate using Next or Do.
}

Output:

type ClientConfig 

type ClientConfig struct {
	// NumChannels is the number of gRPC channels.
	// If zero, a reasonable default is used based on the execution environment.
	NumChannels int

	// SessionPoolConfig is the configuration for session pool.
	SessionPoolConfig
	// SessionLabels for the sessions created by this client.
	// See https://cloud.google.com/spanner/docs/reference/rpc/google.spanner.v1#session for more info.
	SessionLabels map[string]string
	// contains filtered or unexported fields
}

ClientConfig has configurations for the client.

type Error 

type Error struct {
	// Code is the canonical error code for describing the nature of a
	// particular error.
	Code codes.Code
	// Desc explains more details of the error.
	Desc string
	// contains filtered or unexported fields
}

Error is the structured error returned by Cloud Spanner client.

func (*Error) Error 

func (e *Error) Error() string

Error implements error.Error.

type GenericColumnValue 

type GenericColumnValue struct {
	Type  *sppb.Type
	Value *proto3.Value
}

GenericColumnValue represents the generic encoded value and type of the column. See google.spanner.v1.ResultSet proto for details. This can be useful for proxying query results when the result types are not known in advance.

If you populate a GenericColumnValue from a row using Row.Column or related methods, do not modify the contents of Type and Value.

func (GenericColumnValue) Decode 

func (v GenericColumnValue) Decode(ptr interface{}) error

Decode decodes a GenericColumnValue. The ptr argument should be a pointer to a Go value that can accept v.

Example 
package main

import (
	"fmt"

	"cloud.google.com/go/spanner"

	sppb "google.golang.org/genproto/googleapis/spanner/v1"
)

func main() {
	// In real applications, rows can be retrieved by methods like client.Single().ReadRow().
	row, err := spanner.NewRow([]string{"intCol", "strCol"}, []interface{}{42, "my-text"})
	if err != nil {
		// TODO: Handle error.
	}
	for i := 0; i < row.Size(); i++ {
		var col spanner.GenericColumnValue
		if err := row.Column(i, &col); err != nil {
			// TODO: Handle error.
		}
		switch col.Type.Code {
		case sppb.TypeCode_INT64:
			var v int64
			if err := col.Decode(&v); err != nil {
				// TODO: Handle error.
			}
			fmt.Println("int", v)
		case sppb.TypeCode_STRING:
			var v string
			if err := col.Decode(&v); err != nil {
				// TODO: Handle error.
			}
			fmt.Println("string", v)
		}
	}
}

Output:

int 42
string my-text

type Key 

type Key []interface{}

A Key can be either a Cloud Spanner row's primary key or a secondary index key. It is essentially an interface{} array, which represents a set of Cloud Spanner columns. A Key can be used as:

  • A primary key which uniquely identifies a Cloud Spanner row.
  • A secondary index key which maps to a set of Cloud Spanner rows indexed under it.
  • An endpoint of primary key/secondary index ranges; see the KeyRange type.

Rows that are identified by the Key type are outputs of read operation or targets of delete operation in a mutation. Note that for Insert/Update/InsertOrUpdate/Update mutation types, although they don't require a primary key explicitly, the column list provided must contain enough columns that can comprise a primary key.

Keys are easy to construct. For example, suppose you have a table with a primary key of username and product ID. To make a key for this table: 

key := spanner.Key{"john", 16}

See the description of Row and Mutation types for how Go types are mapped to Cloud Spanner types. For convenience, Key type supports a wide range of Go types:

  • int, int8, int16, int32, int64, and NullInt64 are mapped to Cloud Spanner's INT64 type.
  • uint8, uint16 and uint32 are also mapped to Cloud Spanner's INT64 type.
  • float32, float64, NullFloat64 are mapped to Cloud Spanner's FLOAT64 type.
  • bool and NullBool are mapped to Cloud Spanner's BOOL type.
  • []byte is mapped to Cloud Spanner's BYTES type.
  • string and NullString are mapped to Cloud Spanner's STRING type.
  • time.Time and NullTime are mapped to Cloud Spanner's TIMESTAMP type.
  • civil.Date and NullDate are mapped to Cloud Spanner's DATE type.

func (Key) AsPrefix added in v0.8.0 

func (key Key) AsPrefix() KeyRange

AsPrefix returns a KeyRange for all keys where k is the prefix.

func (Key) String 

func (key Key) String() string

String implements fmt.Stringer for Key. For string, []byte and NullString, it prints the uninterpreted bytes of their contents, leaving caller with the opportunity to escape the output.

type KeyRange 

type KeyRange struct {
	// Start specifies the left boundary of the key range; End specifies
	// the right boundary of the key range.
	Start, End Key

	// Kind describes whether the boundaries of the key range include
	// their keys.
	Kind KeyRangeKind
}

A KeyRange represents a range of rows in a table or index.

A range has a Start key and an End key. IncludeStart and IncludeEnd indicate whether the Start and End keys are included in the range.

For example, consider the following table definition: 

CREATE TABLE UserEvents (
  UserName STRING(MAX),
  EventDate STRING(10),
) PRIMARY KEY(UserName, EventDate);

The following keys name rows in this table: 

spanner.Key{"Bob", "2014-09-23"}
spanner.Key{"Alfred", "2015-06-12"}

Since the UserEvents table's PRIMARY KEY clause names two columns, each UserEvents key has two elements; the first is the UserName, and the second is the EventDate.

Key ranges with multiple components are interpreted lexicographically by component using the table or index key's declared sort order. For example, the following range returns all events for user "Bob" that occurred in the year 2015: 

spanner.KeyRange{
	Start: spanner.Key{"Bob", "2015-01-01"},
	End:   spanner.Key{"Bob", "2015-12-31"},
	Kind:  ClosedClosed,
}

Start and end keys can omit trailing key components. This affects the inclusion and exclusion of rows that exactly match the provided key components: if IncludeStart is true, then rows that exactly match the provided components of the Start key are included; if IncludeStart is false then rows that exactly match are not included. IncludeEnd and End key behave in the same fashion.

For example, the following range includes all events for "Bob" that occurred during and after the year 2000: 

spanner.KeyRange{
	Start: spanner.Key{"Bob", "2000-01-01"},
	End:   spanner.Key{"Bob"},
	Kind:  ClosedClosed,
}

The next example retrieves all events for "Bob": 

spanner.Key{"Bob"}.AsPrefix()

To retrieve events before the year 2000: 

spanner.KeyRange{
	Start: spanner.Key{"Bob"},
	End:   spanner.Key{"Bob", "2000-01-01"},
	Kind:  ClosedOpen,
}

Although we specified a Kind for this KeyRange, we didn't need to, because the default is ClosedOpen. In later examples we'll omit Kind if it is ClosedOpen.

The following range includes all rows in a table or under a index: 

spanner.AllKeys()

This range returns all users whose UserName begins with any character from A to C: 

spanner.KeyRange{
	Start: spanner.Key{"A"},
	End:   spanner.Key{"D"},
}

This range returns all users whose UserName begins with B: 

spanner.KeyRange{
	Start: spanner.Key{"B"},
	End:   spanner.Key{"C"},
}

Key ranges honor column sort order. For example, suppose a table is defined as follows: 

CREATE TABLE DescendingSortedTable {
  Key INT64,
  ...
) PRIMARY KEY(Key DESC);

The following range retrieves all rows with key values between 1 and 100 inclusive: 

spanner.KeyRange{
	Start: spanner.Key{100},
	End:   spanner.Key{1},
	Kind:  ClosedClosed,
}

Note that 100 is passed as the start, and 1 is passed as the end, because Key is a descending column in the schema.

func (KeyRange) String 

func (r KeyRange) String() string

String implements fmt.Stringer for KeyRange type.

type KeyRangeKind 

type KeyRangeKind int

KeyRangeKind describes the kind of interval represented by a KeyRange: whether it is open or closed on the left and right. 

const (
	// ClosedOpen is closed on the left and open on the right: the Start
	// key is included, the End key is excluded.
	ClosedOpen KeyRangeKind = iota

	// ClosedClosed is closed on the left and the right: both keys are included.
	ClosedClosed

	// OpenClosed is open on the left and closed on the right: the Start
	// key is excluded, the End key is included.
	OpenClosed

	// OpenOpen is open on the left and the right: neither key is included.
	OpenOpen
)

type KeySet 

type KeySet interface {
	// contains filtered or unexported methods
}

A KeySet defines a collection of Cloud Spanner keys and/or key ranges. All the keys are expected to be in the same table or index. The keys need not be sorted in any particular way.

An individual Key can act as a KeySet, as can a KeyRange. Use the KeySets function to create a KeySet consisting of multiple Keys and KeyRanges. To obtain an empty KeySet, call KeySets with no arguments.

If the same key is specified multiple times in the set (for example if two ranges, two keys, or a key and a range overlap), the Cloud Spanner backend behaves as if the key were only specified once.

func AllKeys 

func AllKeys() KeySet

AllKeys returns a KeySet that represents all Keys of a table or a index.

func KeySets added in v0.8.0 

func KeySets(keySets ...KeySet) KeySet

KeySets returns the union of the KeySets. If any of the KeySets is AllKeys, then the resulting KeySet will be equivalent to AllKeys.

type Mutation 

type Mutation struct {
	// contains filtered or unexported fields
}

A Mutation describes a modification to one or more Cloud Spanner rows. The mutation represents an insert, update, delete, etc on a table.

Many mutations can be applied in a single atomic commit. For purposes of constraint checking (such as foreign key constraints), the operations can be viewed as applying in the same order as the mutations are provided (so that, e.g., a row and its logical "child" can be inserted in the same commit).

The Apply function applies series of mutations. For example, 

 m := spanner.Insert("User",
	 []string{"user_id", "profile"},
	 []interface{}{UserID, profile})
 _, err := client.Apply(ctx, []*spanner.Mutation{m})

inserts a new row into the User table. The primary key for the new row is UserID (presuming that "user_id" has been declared as the primary key of the "User" table).

To apply a series of mutations as part of an atomic read-modify-write operation, use ReadWriteTransaction.

Updating a row

Changing the values of columns in an existing row is very similar to inserting a new row: 

m := spanner.Update("User",
	[]string{"user_id", "profile"},
	[]interface{}{UserID, profile})
_, err := client.Apply(ctx, []*spanner.Mutation{m})

Deleting a row

To delete a row, use spanner.Delete: 

m := spanner.Delete("User", spanner.Key{UserId})
_, err := client.Apply(ctx, []*spanner.Mutation{m})

spanner.Delete accepts a KeySet, so you can also pass in a KeyRange, or use the spanner.KeySets function to build any combination of Keys and KeyRanges.

Note that deleting a row in a table may also delete rows from other tables if cascading deletes are specified in those tables' schemas. Delete does nothing if the named row does not exist (does not yield an error).

Deleting a field

To delete/clear a field within a row, use spanner.Update with the value nil: 

m := spanner.Update("User",
	[]string{"user_id", "profile"},
	[]interface{}{UserID, nil})
_, err := client.Apply(ctx, []*spanner.Mutation{m})

The valid Go types and their corresponding Cloud Spanner types that can be used in the Insert/Update/InsertOrUpdate functions are: 

string, NullString - STRING
[]string, []NullString - STRING ARRAY
[]byte - BYTES
[][]byte - BYTES ARRAY
int, int64, NullInt64 - INT64
[]int, []int64, []NullInt64 - INT64 ARRAY
bool, NullBool - BOOL
[]bool, []NullBool - BOOL ARRAY
float64, NullFloat64 - FLOAT64
[]float64, []NullFloat64 - FLOAT64 ARRAY
time.Time, NullTime - TIMESTAMP
[]time.Time, []NullTime - TIMESTAMP ARRAY
Date, NullDate - DATE
[]Date, []NullDate - DATE ARRAY

To compare two Mutations for testing purposes, use reflect.DeepEqual.

func Delete 

func Delete(table string, ks KeySet) *Mutation

Delete removes the rows described by the KeySet from the table. It succeeds whether or not the keys were present.

Example 
package main

import (
	"cloud.google.com/go/spanner"
)

func main() {
	m := spanner.Delete("Users", spanner.Key{"alice"})
	_ = m // TODO: use with Client.Apply or in a ReadWriteTransaction.
}

Output:
Example (KeyRange) 
package main

import (
	"cloud.google.com/go/spanner"
)

func main() {
	m := spanner.Delete("Users", spanner.KeyRange{
		Start: spanner.Key{"alice"},
		End:   spanner.Key{"bob"},
		Kind:  spanner.ClosedClosed,
	})
	_ = m // TODO: use with Client.Apply or in a ReadWriteTransaction.
}

Output:

func Insert 

func Insert(table string, cols []string, vals []interface{}) *Mutation

Insert returns a Mutation to insert a row into a table. If the row already exists, the write or transaction fails.

Example 
package main

import (
	"cloud.google.com/go/spanner"
)

func main() {
	m := spanner.Insert("Users", []string{"name", "email"}, []interface{}{"alice", "a@example.com"})
	_ = m // TODO: use with Client.Apply or in a ReadWriteTransaction.
}

Output:

func InsertMap 

func InsertMap(table string, in map[string]interface{}) *Mutation

InsertMap returns a Mutation to insert a row into a table, specified by a map of column name to value. If the row already exists, the write or transaction fails.

Example 
package main

import (
	"cloud.google.com/go/spanner"
)

func main() {
	m := spanner.InsertMap("Users", map[string]interface{}{
		"name":  "alice",
		"email": "a@example.com",
	})
	_ = m // TODO: use with Client.Apply or in a ReadWriteTransaction.
}

Output:

func InsertOrUpdate 

func InsertOrUpdate(table string, cols []string, vals []interface{}) *Mutation

InsertOrUpdate returns a Mutation to insert a row into a table. If the row already exists, it updates it instead. Any column values not explicitly written are preserved.

For a similar example, See Update.

func InsertOrUpdateMap 

func InsertOrUpdateMap(table string, in map[string]interface{}) *Mutation

InsertOrUpdateMap returns a Mutation to insert a row into a table, specified by a map of column to value. If the row already exists, it updates it instead. Any column values not explicitly written are preserved.

For a similar example, See UpdateMap.

func InsertOrUpdateStruct 

func InsertOrUpdateStruct(table string, in interface{}) (*Mutation, error)

InsertOrUpdateStruct returns a Mutation to insert a row into a table, specified by a Go struct. If the row already exists, it updates it instead. Any column values not explicitly written are preserved.

The in argument must be a struct or a pointer to a struct. Its exported fields specify the column names and values. Use a field tag like "spanner:name" to provide an alternative column name, or use "spanner:-" to ignore the field.

For a similar example, See UpdateStruct.

func InsertStruct 

func InsertStruct(table string, in interface{}) (*Mutation, error)

InsertStruct returns a Mutation to insert a row into a table, specified by a Go struct. If the row already exists, the write or transaction fails.

The in argument must be a struct or a pointer to a struct. Its exported fields specify the column names and values. Use a field tag like "spanner:name" to provide an alternative column name, or use "spanner:-" to ignore the field.

Example 
package main

import (
	"cloud.google.com/go/spanner"
)

func main() {
	type User struct {
		Name, Email string
	}
	u := User{Name: "alice", Email: "a@example.com"}
	m, err := spanner.InsertStruct("Users", u)
	if err != nil {
		// TODO: Handle error.
	}
	_ = m // TODO: use with Client.Apply or in a ReadWriteTransaction.
}

Output:

func Replace 

func Replace(table string, cols []string, vals []interface{}) *Mutation

Replace returns a Mutation to insert a row into a table, deleting any existing row. Unlike InsertOrUpdate, this means any values not explicitly written become NULL.

For a similar example, See Update.

func ReplaceMap 

func ReplaceMap(table string, in map[string]interface{}) *Mutation

ReplaceMap returns a Mutation to insert a row into a table, deleting any existing row. Unlike InsertOrUpdateMap, this means any values not explicitly written become NULL. The row is specified by a map of column to value.

For a similar example, See UpdateMap.

func ReplaceStruct 

func ReplaceStruct(table string, in interface{}) (*Mutation, error)

ReplaceStruct returns a Mutation to insert a row into a table, deleting any existing row. Unlike InsertOrUpdateMap, this means any values not explicitly written become NULL. The row is specified by a Go struct.

The in argument must be a struct or a pointer to a struct. Its exported fields specify the column names and values. Use a field tag like "spanner:name" to provide an alternative column name, or use "spanner:-" to ignore the field.

For a similar example, See UpdateStruct.

func Update 

func Update(table string, cols []string, vals []interface{}) *Mutation

Update returns a Mutation to update a row in a table. If the row does not already exist, the write or transaction fails.

Example 
package main

import (
	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	_, err = client.ReadWriteTransaction(ctx, func(ctx context.Context, txn *spanner.ReadWriteTransaction) error {
		row, err := txn.ReadRow(ctx, "Accounts", spanner.Key{"alice"}, []string{"balance"})
		if err != nil {
			return err
		}
		var balance int64
		if err := row.Column(0, &balance); err != nil {
			return err
		}
		return txn.BufferWrite([]*spanner.Mutation{
			spanner.Update("Accounts", []string{"user", "balance"}, []interface{}{"alice", balance + 10}),
		})
	})
	if err != nil {
		// TODO: Handle error.
	}
}

Output:

func UpdateMap 

func UpdateMap(table string, in map[string]interface{}) *Mutation

UpdateMap returns a Mutation to update a row in a table, specified by a map of column to value. If the row does not already exist, the write or transaction fails.

Example

This example is the same as the one for Update, except for the use of UpdateMap. 

package main

import (
	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	_, err = client.ReadWriteTransaction(ctx, func(ctx context.Context, txn *spanner.ReadWriteTransaction) error {
		row, err := txn.ReadRow(ctx, "Accounts", spanner.Key{"alice"}, []string{"balance"})
		if err != nil {
			return err
		}
		var balance int64
		if err := row.Column(0, &balance); err != nil {
			return err
		}
		return txn.BufferWrite([]*spanner.Mutation{
			spanner.UpdateMap("Accounts", map[string]interface{}{
				"user":    "alice",
				"balance": balance + 10,
			}),
		})
	})
	if err != nil {
		// TODO: Handle error.
	}
}

Output:

func UpdateStruct 

func UpdateStruct(table string, in interface{}) (*Mutation, error)

UpdateStruct returns a Mutation to update a row in a table, specified by a Go struct. If the row does not already exist, the write or transaction fails.

Example

This example is the same as the one for Update, except for the use of UpdateStruct. 

package main

import (
	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	type account struct {
		User    string `spanner:"user"`
		Balance int64  `spanner:"balance"`
	}
	_, err = client.ReadWriteTransaction(ctx, func(ctx context.Context, txn *spanner.ReadWriteTransaction) error {
		row, err := txn.ReadRow(ctx, "Accounts", spanner.Key{"alice"}, []string{"balance"})
		if err != nil {
			return err
		}
		var balance int64
		if err := row.Column(0, &balance); err != nil {
			return err
		}
		m, err := spanner.UpdateStruct("Accounts", account{
			User:    "alice",
			Balance: balance + 10,
		})
		if err != nil {
			return err
		}
		return txn.BufferWrite([]*spanner.Mutation{m})
	})
	if err != nil {
		// TODO: Handle error.
	}
}

Output:

type NullBool 

type NullBool struct {
	Bool  bool
	Valid bool // Valid is true if Bool is not NULL.
}

NullBool represents a Cloud Spanner BOOL that may be NULL.

func (NullBool) String 

func (n NullBool) String() string

String implements Stringer.String for NullBool

type NullDate 

type NullDate struct {
	Date  civil.Date
	Valid bool // Valid is true if Date is not NULL.
}

NullDate represents a Cloud Spanner DATE that may be null.

func (NullDate) String 

func (n NullDate) String() string

String implements Stringer.String for NullDate

type NullFloat64 

type NullFloat64 struct {
	Float64 float64
	Valid   bool // Valid is true if Float64 is not NULL.
}

NullFloat64 represents a Cloud Spanner FLOAT64 that may be NULL.

func (NullFloat64) String 

func (n NullFloat64) String() string

String implements Stringer.String for NullFloat64

type NullInt64 

type NullInt64 struct {
	Int64 int64
	Valid bool // Valid is true if Int64 is not NULL.
}

NullInt64 represents a Cloud Spanner INT64 that may be NULL.

func (NullInt64) String 

func (n NullInt64) String() string

String implements Stringer.String for NullInt64

type NullRow 

type NullRow struct {
	Row   Row
	Valid bool // Valid is true if Row is not NULL.
}

NullRow represents a Cloud Spanner STRUCT that may be NULL. See also the document for Row. Note that NullRow is not a valid Cloud Spanner column Type.

type NullString 

type NullString struct {
	StringVal string
	Valid     bool // Valid is true if StringVal is not NULL.
}

NullString represents a Cloud Spanner STRING that may be NULL.

func (NullString) String 

func (n NullString) String() string

String implements Stringer.String for NullString

type NullTime 

type NullTime struct {
	Time  time.Time
	Valid bool // Valid is true if Time is not NULL.
}

NullTime represents a Cloud Spanner TIMESTAMP that may be null.

func (NullTime) String 

func (n NullTime) String() string

String implements Stringer.String for NullTime

type Partition added in v0.20.0 

type Partition struct {
	// contains filtered or unexported fields
}

Partition defines a segment of data to be read in a batch read or query. A partition can be serialized and processed across several different machines or processes.

func (Partition) MarshalBinary added in v0.20.0 

func (p Partition) MarshalBinary() (data []byte, err error)

MarshalBinary implements BinaryMarshaler.

func (*Partition) UnmarshalBinary added in v0.20.0 

func (p *Partition) UnmarshalBinary(data []byte) error

UnmarshalBinary implements BinaryUnmarshaler.

type PartitionOptions added in v0.20.0 

type PartitionOptions struct {
	// The desired data size for each partition generated.
	PartitionBytes int64
	// The desired maximum number of partitions to return.
	MaxPartitions int64
}

PartitionOptions specifies options for a PartitionQueryRequest and PartitionReadRequest. See https://godoc.org/google.golang.org/genproto/googleapis/spanner/v1#PartitionOptions for more details.

type ReadOnlyTransaction 

type ReadOnlyTransaction struct {
	// contains filtered or unexported fields
}

ReadOnlyTransaction provides a snapshot transaction with guaranteed consistency across reads, but does not allow writes. Read-only transactions can be configured to read at timestamps in the past.

Read-only transactions do not take locks. Instead, they work by choosing a Cloud Spanner timestamp, then executing all reads at that timestamp. Since they do not acquire locks, they do not block concurrent read-write transactions.

Unlike locking read-write transactions, read-only transactions never abort. They can fail if the chosen read timestamp is garbage collected; however, the default garbage collection policy is generous enough that most applications do not need to worry about this in practice. See the documentation of TimestampBound for more details.

A ReadOnlyTransaction consumes resources on the server until Close is called.

func (*ReadOnlyTransaction) AnalyzeQuery added in v0.18.0 

func (t *ReadOnlyTransaction) AnalyzeQuery(ctx context.Context, statement Statement) (*sppb.QueryPlan, error)

AnalyzeQuery returns the query plan for statement.

func (*ReadOnlyTransaction) Close 

func (t *ReadOnlyTransaction) Close()

Close closes a ReadOnlyTransaction, the transaction cannot perform any reads after being closed.

func (*ReadOnlyTransaction) Query 

func (t *ReadOnlyTransaction) Query(ctx context.Context, statement Statement) *RowIterator

Query executes a query against the database. It returns a RowIterator for retrieving the resulting rows.

Query returns only row data, without a query plan or execution statistics. Use QueryWithStats to get rows along with the plan and statistics. Use AnalyzeQuery to get just the plan.

Example 
package main

import (
	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	iter := client.Single().Query(ctx, spanner.NewStatement("SELECT FirstName FROM Singers"))
	_ = iter // TODO: iterate using Next or Do.
}

Output:

func (*ReadOnlyTransaction) QueryWithStats added in v0.18.0 

func (t *ReadOnlyTransaction) QueryWithStats(ctx context.Context, statement Statement) *RowIterator

Query executes a SQL statement against the database. It returns a RowIterator for retrieving the resulting rows. The RowIterator will also be populated with a query plan and execution statistics.

func (*ReadOnlyTransaction) Read 

func (t *ReadOnlyTransaction) Read(ctx context.Context, table string, keys KeySet, columns []string) *RowIterator

Read returns a RowIterator for reading multiple rows from the database.

Example 
package main

import (
	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	iter := client.Single().Read(ctx, "Users",
		spanner.KeySets(spanner.Key{"alice"}, spanner.Key{"bob"}),
		[]string{"name", "email"})
	_ = iter // TODO: iterate using Next or Do.
}

Output:

func (*ReadOnlyTransaction) ReadRow 

func (t *ReadOnlyTransaction) ReadRow(ctx context.Context, table string, key Key, columns []string) (*Row, error)

ReadRow reads a single row from the database.

If no row is present with the given key, then ReadRow returns an error where spanner.ErrCode(err) is codes.NotFound.

Example 
package main

import (
	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	row, err := client.Single().ReadRow(ctx, "Users", spanner.Key{"alice"},
		[]string{"name", "email"})
	if err != nil {
		// TODO: Handle error.
	}
	_ = row // TODO: use row
}

Output:

func (*ReadOnlyTransaction) ReadUsingIndex 

func (t *ReadOnlyTransaction) ReadUsingIndex(ctx context.Context, table, index string, keys KeySet, columns []string) (ri *RowIterator)

ReadUsingIndex calls ReadWithOptions with ReadOptions{Index: index}.

Example 
package main

import (
	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	iter := client.Single().ReadUsingIndex(ctx, "Users",
		"UsersByEmail",
		spanner.KeySets(spanner.Key{"a@example.com"}, spanner.Key{"b@example.com"}),
		[]string{"name", "email"})
	_ = iter // TODO: iterate using Next or Do.
}

Output:

func (*ReadOnlyTransaction) ReadWithOptions added in v0.18.0 

func (t *ReadOnlyTransaction) ReadWithOptions(ctx context.Context, table string, keys KeySet, columns []string, opts *ReadOptions) (ri *RowIterator)

ReadWithOptions returns a RowIterator for reading multiple rows from the database. Pass a ReadOptions to modify the read operation.

Example 
package main

import (
	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	// Use an index, and limit to 100 rows at most.
	iter := client.Single().ReadWithOptions(ctx, "Users",
		spanner.KeySets(spanner.Key{"a@example.com"}, spanner.Key{"b@example.com"}),
		[]string{"name", "email"}, &spanner.ReadOptions{
			Index: "UsersByEmail",
			Limit: 100,
		})
	_ = iter // TODO: iterate using Next or Do.
}

Output:

func (*ReadOnlyTransaction) Timestamp 

func (t *ReadOnlyTransaction) Timestamp() (time.Time, error)

Timestamp returns the timestamp chosen to perform reads and queries in this transaction. The value can only be read after some read or query has either returned some data or completed without returning any data.

Example 
package main

import (
	"fmt"

	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	txn := client.Single()
	row, err := txn.ReadRow(ctx, "Users", spanner.Key{"alice"},
		[]string{"name", "email"})
	if err != nil {
		// TODO: Handle error.
	}
	readTimestamp, err := txn.Timestamp()
	if err != nil {
		// TODO: Handle error.
	}
	fmt.Println("read happened at", readTimestamp)
	_ = row // TODO: use row
}

Output:

func (*ReadOnlyTransaction) WithTimestampBound 

func (t *ReadOnlyTransaction) WithTimestampBound(tb TimestampBound) *ReadOnlyTransaction

WithTimestampBound specifies the TimestampBound to use for read or query. This can only be used before the first read or query is invoked. Note: bounded staleness is not available with general ReadOnlyTransactions; use a single-use ReadOnlyTransaction instead.

The returned value is the ReadOnlyTransaction so calls can be chained.

Example 
package main

import (
	"fmt"
	"time"

	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	txn := client.Single().WithTimestampBound(spanner.MaxStaleness(30 * time.Second))
	row, err := txn.ReadRow(ctx, "Users", spanner.Key{"alice"}, []string{"name", "email"})
	if err != nil {
		// TODO: Handle error.
	}
	_ = row // TODO: use row
	readTimestamp, err := txn.Timestamp()
	if err != nil {
		// TODO: Handle error.
	}
	fmt.Println("read happened at", readTimestamp)
}

Output:

type ReadOptions added in v0.18.0 

type ReadOptions struct {
	// The index to use for reading. If non-empty, you can only read columns that are
	// part of the index key, part of the primary key, or stored in the index due to
	// a STORING clause in the index definition.
	Index string

	// The maximum number of rows to read. A limit value less than 1 means no limit.
	Limit int
}

ReadOptions provides options for reading rows from a database.

type ReadWriteTransaction 

type ReadWriteTransaction struct {
	// contains filtered or unexported fields
}

ReadWriteTransaction provides a locking read-write transaction.

This type of transaction is the only way to write data into Cloud Spanner; (*Client).Apply and (*Client).ApplyAtLeastOnce use transactions internally. These transactions rely on pessimistic locking and, if necessary, two-phase commit. Locking read-write transactions may abort, requiring the application to retry. However, the interface exposed by (*Client).ReadWriteTransaction eliminates the need for applications to write retry loops explicitly.

Locking transactions may be used to atomically read-modify-write data anywhere in a database. This type of transaction is externally consistent.

Clients should attempt to minimize the amount of time a transaction is active. Faster transactions commit with higher probability and cause less contention. Cloud Spanner attempts to keep read locks active as long as the transaction continues to do reads. Long periods of inactivity at the client may cause Cloud Spanner to release a transaction's locks and abort it.

Reads performed within a transaction acquire locks on the data being read. Writes can only be done at commit time, after all reads have been completed. Conceptually, a read-write transaction consists of zero or more reads or SQL queries followed by a commit.

See (*Client).ReadWriteTransaction for an example.

Semantics

Cloud Spanner can commit the transaction if all read locks it acquired are still valid at commit time, and it is able to acquire write locks for all writes. Cloud Spanner can abort the transaction for any reason. If a commit attempt returns ABORTED, Cloud Spanner guarantees that the transaction has not modified any user data in Cloud Spanner.

Unless the transaction commits, Cloud Spanner makes no guarantees about how long the transaction's locks were held for. It is an error to use Cloud Spanner locks for any sort of mutual exclusion other than between Cloud Spanner transactions themselves.

Aborted transactions

Application code does not need to retry explicitly; RunInTransaction will automatically retry a transaction if an attempt results in an abort. The lock priority of a transaction increases after each prior aborted transaction, meaning that the next attempt has a slightly better chance of success than before.

Under some circumstances (e.g., many transactions attempting to modify the same row(s)), a transaction can abort many times in a short period before successfully committing. Thus, it is not a good idea to cap the number of retries a transaction can attempt; instead, it is better to limit the total amount of wall time spent retrying.

Idle transactions

A transaction is considered idle if it has no outstanding reads or SQL queries and has not started a read or SQL query within the last 10 seconds. Idle transactions can be aborted by Cloud Spanner so that they don't hold on to locks indefinitely. In that case, the commit will fail with error ABORTED.

If this behavior is undesirable, periodically executing a simple SQL query in the transaction (e.g., SELECT 1) prevents the transaction from becoming idle.

func (*ReadWriteTransaction) AnalyzeQuery added in v0.18.0 

func (t *ReadWriteTransaction) AnalyzeQuery(ctx context.Context, statement Statement) (*sppb.QueryPlan, error)

AnalyzeQuery returns the query plan for statement.

func (*ReadWriteTransaction) BufferWrite 

func (t *ReadWriteTransaction) BufferWrite(ms []*Mutation) error

BufferWrite adds a list of mutations to the set of updates that will be applied when the transaction is committed. It does not actually apply the write until the transaction is committed, so the operation does not block. The effects of the write won't be visible to any reads (including reads done in the same transaction) until the transaction commits.

See the example for Client.ReadWriteTransaction.

func (*ReadWriteTransaction) Query 

func (t *ReadWriteTransaction) Query(ctx context.Context, statement Statement) *RowIterator

Query executes a query against the database. It returns a RowIterator for retrieving the resulting rows.

Query returns only row data, without a query plan or execution statistics. Use QueryWithStats to get rows along with the plan and statistics. Use AnalyzeQuery to get just the plan.

func (*ReadWriteTransaction) QueryWithStats added in v0.18.0 

func (t *ReadWriteTransaction) QueryWithStats(ctx context.Context, statement Statement) *RowIterator

Query executes a SQL statement against the database. It returns a RowIterator for retrieving the resulting rows. The RowIterator will also be populated with a query plan and execution statistics.

func (*ReadWriteTransaction) Read 

func (t *ReadWriteTransaction) Read(ctx context.Context, table string, keys KeySet, columns []string) *RowIterator

Read returns a RowIterator for reading multiple rows from the database.

func (*ReadWriteTransaction) ReadRow 

func (t *ReadWriteTransaction) ReadRow(ctx context.Context, table string, key Key, columns []string) (*Row, error)

ReadRow reads a single row from the database.

If no row is present with the given key, then ReadRow returns an error where spanner.ErrCode(err) is codes.NotFound.

func (*ReadWriteTransaction) ReadUsingIndex 

func (t *ReadWriteTransaction) ReadUsingIndex(ctx context.Context, table, index string, keys KeySet, columns []string) (ri *RowIterator)

ReadUsingIndex calls ReadWithOptions with ReadOptions{Index: index}.

func (*ReadWriteTransaction) ReadWithOptions added in v0.18.0 

func (t *ReadWriteTransaction) ReadWithOptions(ctx context.Context, table string, keys KeySet, columns []string, opts *ReadOptions) (ri *RowIterator)

ReadWithOptions returns a RowIterator for reading multiple rows from the database. Pass a ReadOptions to modify the read operation.

func (*ReadWriteTransaction) Update added in v0.30.0 

func (t *ReadWriteTransaction) Update(ctx context.Context, stmt Statement) (rowCount int64, err error)

Update executes a DML statement against the database. It returns the number of affected rows. Update returns an error if the statement is a query. However, the query is executed, and any data read will be validated upon commit.

type Row 

type Row struct {
	// contains filtered or unexported fields
}

A Row is a view of a row of data returned by a Cloud Spanner read. It consists of a number of columns; the number depends on the columns used to construct the read.

The column values can be accessed by index. For instance, if the read specified []string{"photo_id", "caption"}, then each row will contain two columns: "photo_id" with index 0, and "caption" with index 1.

Column values are decoded by using one of the Column, ColumnByName, or Columns methods. The valid values passed to these methods depend on the column type. For example: 

var photoID int64
err := row.Column(0, &photoID) // Decode column 0 as an integer.

var caption string
err := row.Column(1, &caption) // Decode column 1 as a string.

// Decode all the columns.
err := row.Columns(&photoID, &caption)

Supported types and their corresponding Cloud Spanner column type(s) are: 

*string(not NULL), *NullString - STRING
*[]string, *[]NullString - STRING ARRAY
*[]byte - BYTES
*[][]byte - BYTES ARRAY
*int64(not NULL), *NullInt64 - INT64
*[]int64, *[]NullInt64 - INT64 ARRAY
*bool(not NULL), *NullBool - BOOL
*[]bool, *[]NullBool - BOOL ARRAY
*float64(not NULL), *NullFloat64 - FLOAT64
*[]float64, *[]NullFloat64 - FLOAT64 ARRAY
*time.Time(not NULL), *NullTime - TIMESTAMP
*[]time.Time, *[]NullTime - TIMESTAMP ARRAY
*Date(not NULL), *NullDate - DATE
*[]civil.Date, *[]NullDate - DATE ARRAY
*[]*some_go_struct, *[]NullRow - STRUCT ARRAY
*GenericColumnValue - any Cloud Spanner type

For TIMESTAMP columns, the returned time.Time object will be in UTC.

To fetch an array of BYTES, pass a *[][]byte. To fetch an array of (sub)rows, pass a *[]spanner.NullRow or a *[]*some_go_struct where some_go_struct holds all information of the subrow, see spanner.Row.ToStruct for the mapping between a Cloud Spanner row and a Go struct. To fetch an array of other types, pass a *[]spanner.NullXXX type of the appropriate type. Use GenericColumnValue when you don't know in advance what column type to expect.

Row decodes the row contents lazily; as a result, each call to a getter has a chance of returning an error.

A column value may be NULL if the corresponding value is not present in Cloud Spanner. The spanner.NullXXX types (spanner.NullInt64 et al.) allow fetching values that may be null. A NULL BYTES can be fetched into a *[]byte as nil. It is an error to fetch a NULL value into any other type.

func NewRow 

func NewRow(columnNames []string, columnValues []interface{}) (*Row, error)

NewRow returns a Row containing the supplied data. This can be useful for mocking Cloud Spanner Read and Query responses for unit testing.

func (*Row) Column 

func (r *Row) Column(i int, ptr interface{}) error

Column fetches the value from the ith column, decoding it into ptr. See the Row documentation for the list of acceptable argument types. see Client.ReadWriteTransaction for an example.

func (*Row) ColumnByName 

func (r *Row) ColumnByName(name string, ptr interface{}) error

ColumnByName fetches the value from the named column, decoding it into ptr. See the Row documentation for the list of acceptable argument types.

Example 
package main

import (
	"fmt"

	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	row, err := client.Single().ReadRow(ctx, "Accounts", spanner.Key{"alice"}, []string{"name", "balance"})
	if err != nil {
		// TODO: Handle error.
	}
	var balance int64
	if err := row.ColumnByName("balance", &balance); err != nil {
		// TODO: Handle error.
	}
	fmt.Println(balance)
}

Output:

func (*Row) ColumnIndex 

func (r *Row) ColumnIndex(name string) (int, error)

ColumnIndex returns the index of the column with the given name. The comparison is case-sensitive.

Example 
package main

import (
	"fmt"

	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	row, err := client.Single().ReadRow(ctx, "Accounts", spanner.Key{"alice"}, []string{"name", "balance"})
	if err != nil {
		// TODO: Handle error.
	}
	index, err := row.ColumnIndex("balance")
	if err != nil {
		// TODO: Handle error.
	}
	fmt.Println(index)
}

Output:

func (*Row) ColumnName 

func (r *Row) ColumnName(i int) string

ColumnName returns the name of column i, or empty string for invalid column.

Example 
package main

import (
	"fmt"

	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	row, err := client.Single().ReadRow(ctx, "Accounts", spanner.Key{"alice"}, []string{"name", "balance"})
	if err != nil {
		// TODO: Handle error.
	}
	fmt.Println(row.ColumnName(1)) // prints "balance"
}

Output:

func (*Row) ColumnNames 

func (r *Row) ColumnNames() []string

ColumnNames returns all column names of the row.

Example 
package main

import (
	"fmt"

	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	row, err := client.Single().ReadRow(ctx, "Accounts", spanner.Key{"alice"}, []string{"name", "balance"})
	if err != nil {
		// TODO: Handle error.
	}
	fmt.Println(row.ColumnNames())
}

Output:

func (*Row) Columns 

func (r *Row) Columns(ptrs ...interface{}) error

Columns fetches all the columns in the row at once.

The value of the kth column will be decoded into the kth argument to Columns. See Row for the list of acceptable argument types. The number of arguments must be equal to the number of columns. Pass nil to specify that a column should be ignored.

Example 
package main

import (
	"fmt"

	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	row, err := client.Single().ReadRow(ctx, "Accounts", spanner.Key{"alice"}, []string{"name", "balance"})
	if err != nil {
		// TODO: Handle error.
	}
	var name string
	var balance int64
	if err := row.Columns(&name, &balance); err != nil {
		// TODO: Handle error.
	}
	fmt.Println(name, balance)
}

Output:

func (*Row) Size 

func (r *Row) Size() int

Size is the number of columns in the row.

Example 
package main

import (
	"fmt"

	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	row, err := client.Single().ReadRow(ctx, "Accounts", spanner.Key{"alice"}, []string{"name", "balance"})
	if err != nil {
		// TODO: Handle error.
	}
	fmt.Println(row.Size()) // size is 2
}

Output:

func (*Row) ToStruct 

func (r *Row) ToStruct(p interface{}) error

ToStruct fetches the columns in a row into the fields of a struct. The rules for mapping a row's columns into a struct's exported fields are:

  1. If a field has a `spanner: "column_name"` tag, then decode column 'column_name' into the field. A special case is the `spanner: "-"` tag, which instructs ToStruct to ignore the field during decoding.

  2. Otherwise, if the name of a field matches the name of a column (ignoring case), decode the column into the field.

The fields of the destination struct can be of any type that is acceptable to spanner.Row.Column.

Slice and pointer fields will be set to nil if the source column is NULL, and a non-nil value if the column is not NULL. To decode NULL values of other types, use one of the spanner.NullXXX types as the type of the destination field.

If ToStruct returns an error, the contents of p are undefined. Some fields may have been successfully populated, while others were not; you should not use any of the fields.

Example 
package main

import (
	"fmt"

	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	row, err := client.Single().ReadRow(ctx, "Accounts", spanner.Key{"alice"}, []string{"name", "balance"})
	if err != nil {
		// TODO: Handle error.
	}

	type Account struct {
		Name    string
		Balance int64
	}

	var acct Account
	if err := row.ToStruct(&acct); err != nil {
		// TODO: Handle error.
	}
	fmt.Println(acct)
}

Output:

type RowIterator 

type RowIterator struct {
	// The plan for the query. Available after RowIterator.Next returns iterator.Done
	// if QueryWithStats was called.
	QueryPlan *sppb.QueryPlan

	// Execution statistics for the query. Available after RowIterator.Next returns iterator.Done
	// if QueryWithStats was called.
	QueryStats map[string]interface{}

	// For a DML statement, the number of rows affected. For PDML, this is a lower bound.
	// Available for DML statements after RowIterator.Next returns iterator.Done.
	RowCount int64
	// contains filtered or unexported fields
}

RowIterator is an iterator over Rows.

func (*RowIterator) Do 

func (r *RowIterator) Do(f func(r *Row) error) error

Do calls the provided function once in sequence for each row in the iteration. If the function returns a non-nil error, Do immediately returns that error.

If there are no rows in the iterator, Do will return nil without calling the provided function.

Do always calls Stop on the iterator.

Example 
package main

import (
	"fmt"

	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	iter := client.Single().Query(ctx, spanner.NewStatement("SELECT FirstName FROM Singers"))
	err = iter.Do(func(r *spanner.Row) error {
		var firstName string
		if err := r.Column(0, &firstName); err != nil {
			return err
		}
		fmt.Println(firstName)
		return nil
	})
	if err != nil {
		// TODO: Handle error.
	}
}

Output:

func (*RowIterator) Next 

func (r *RowIterator) Next() (*Row, error)

Next returns the next result. Its second return value is iterator.Done if there are no more results. Once Next returns Done, all subsequent calls will return Done.

Example 
package main

import (
	"fmt"

	"cloud.google.com/go/spanner"
	"golang.org/x/net/context"
	"google.golang.org/api/iterator"
)

const myDB = "projects/my-project/instances/my-instance/database/my-db"

func main() {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, myDB)
	if err != nil {
		// TODO: Handle error.
	}
	iter := client.Single().Query(ctx, spanner.NewStatement("SELECT FirstName FROM Singers"))
	defer iter.Stop()
	for {
		row, err := iter.Next()
		if err == iterator.Done {
			break
		}
		if err != nil {
			// TODO: Handle error.
		}
		var firstName string
		if err := row.Column(0, &firstName); err != nil {
			// TODO: Handle error.
		}
		fmt.Println(firstName)
	}
}

Output:

func (*RowIterator) Stop 

func (r *RowIterator) Stop()

Stop terminates the iteration. It should be called after you finish using the iterator.

type SessionPoolConfig 

type SessionPoolConfig struct {

	// MaxOpened is the maximum number of opened sessions allowed by the session
	// pool. Defaults to NumChannels * 100. If the client tries to open a session and
	// there are already MaxOpened sessions, it will block until one becomes
	// available or the context passed to the client method is canceled or times out.
	MaxOpened uint64
	// MinOpened is the minimum number of opened sessions that the session pool
	// tries to maintain. Session pool won't continue to expire sessions if number
	// of opened connections drops below MinOpened. However, if a session is found
	// to be broken, it will still be evicted from the session pool, therefore it is
	// posssible that the number of opened sessions drops below MinOpened.
	MinOpened uint64
	// MaxIdle is the maximum number of idle sessions, pool is allowed to keep. Defaults to 0.
	MaxIdle uint64
	// MaxBurst is the maximum number of concurrent session creation requests. Defaults to 10.
	MaxBurst uint64
	// WriteSessions is the fraction of sessions we try to keep prepared for write.
	WriteSessions float64
	// HealthCheckWorkers is number of workers used by health checker for this pool.
	HealthCheckWorkers int
	// HealthCheckInterval is how often the health checker pings a session. Defaults to 5 min.
	HealthCheckInterval time.Duration
	// contains filtered or unexported fields
}

SessionPoolConfig stores configurations of a session pool.

type Statement 

type Statement struct {
	SQL    string
	Params map[string]interface{}
}

A Statement is a SQL query with named parameters.

A parameter placeholder consists of '@' followed by the parameter name. Parameter names consist of any combination of letters, numbers, and underscores. Names may be entirely numeric (e.g., "WHERE m.id = @5"). Parameters may appear anywhere that a literal value is expected. The same parameter name may be used more than once. It is an error to execute a statement with unbound parameters. On the other hand, it is allowable to bind parameter names that are not used.

See the documentation of the Row type for how Go types are mapped to Cloud Spanner types.

func NewStatement 

func NewStatement(sql string) Statement

NewStatement returns a Statement with the given SQL and an empty Params map.

Example 
package main

import (
	"cloud.google.com/go/spanner"
)

func main() {
	stmt := spanner.NewStatement("SELECT FirstName, LastName FROM SINGERS WHERE LastName >= @start")
	stmt.Params["start"] = "Dylan"
	// TODO: Use stmt in Query.
}

Output:
Example (StructLiteral) 
package main

import (
	"cloud.google.com/go/spanner"
)

func main() {
	stmt := spanner.Statement{
		SQL: `SELECT FirstName, LastName FROM SINGERS WHERE LastName = ("Lea", "Martin")`,
	}
	_ = stmt // TODO: Use stmt in Query.
}

Output:

type TimestampBound 

type TimestampBound struct {
	// contains filtered or unexported fields
}

TimestampBound defines how Cloud Spanner will choose a timestamp for a single read/query or read-only transaction.

There are three types of timestamp bound: strong, bounded staleness and exact staleness. Strong is the default.

If the Cloud Spanner database to be read is geographically distributed, stale read-only transactions can execute more quickly than strong or read-write transactions, because they are able to execute far from the leader replica.

Each type of timestamp bound is discussed in detail below. A TimestampBound can be specified when creating transactions, see the documentation of spanner.Client for an example.

Strong reads

Strong reads are guaranteed to see the effects of all transactions that have committed before the start of the read. Furthermore, all rows yielded by a single read are consistent with each other: if any part of the read observes a transaction, all parts of the read see the transaction.

Strong reads are not repeatable: two consecutive strong read-only transactions might return inconsistent results if there are concurrent writes. If consistency across reads is required, the reads should be executed within a transaction or at an exact read timestamp.

Use StrongRead to create a bound of this type.

Exact staleness

An exact staleness timestamp bound executes reads at a user-specified timestamp. Reads at a timestamp are guaranteed to see a consistent prefix of the global transaction history: they observe modifications done by all transactions with a commit timestamp less than or equal to the read timestamp, and observe none of the modifications done by transactions with a larger commit timestamp. They will block until all conflicting transactions that may be assigned commit timestamps less than or equal to the read timestamp have finished.

The timestamp can either be expressed as an absolute Cloud Spanner commit timestamp or a staleness relative to the current time.

These modes do not require a "negotiation phase" to pick a timestamp. As a result, they execute slightly faster than the equivalent boundedly stale concurrency modes. On the other hand, boundedly stale reads usually return fresher results.

Use ReadTimestamp and ExactStaleness to create a bound of this type.

Bounded staleness

Bounded staleness modes allow Cloud Spanner to pick the read timestamp, subject to a user-provided staleness bound. Cloud Spanner chooses the newest timestamp within the staleness bound that allows execution of the reads at the closest available replica without blocking.

All rows yielded are consistent with each other: if any part of the read observes a transaction, all parts of the read see the transaction. Boundedly stale reads are not repeatable: two stale reads, even if they use the same staleness bound, can execute at different timestamps and thus return inconsistent results.

Boundedly stale reads execute in two phases. The first phase negotiates a timestamp among all replicas needed to serve the read. In the second phase, reads are executed at the negotiated timestamp.

As a result of this two-phase execution, bounded staleness reads are usually a little slower than comparable exact staleness reads. However, they are typically able to return fresher results, and are more likely to execute at the closest replica.

Because the timestamp negotiation requires up-front knowledge of which rows will be read, it can only be used with single-use reads and single-use read-only transactions.

Use MinReadTimestamp and MaxStaleness to create a bound of this type.

Old read timestamps and garbage collection

Cloud Spanner continuously garbage collects deleted and overwritten data in the background to reclaim storage space. This process is known as "version GC". By default, version GC reclaims versions after they are four hours old. Because of this, Cloud Spanner cannot perform reads at read timestamps more than four hours in the past. This restriction also applies to in-progress reads and/or SQL queries whose timestamps become too old while executing. Reads and SQL queries with too-old read timestamps fail with the error ErrorCode.FAILED_PRECONDITION.

func ExactStaleness 

func ExactStaleness(d time.Duration) TimestampBound

ExactStaleness returns a TimestampBound that will perform reads and queries at an exact staleness.

func MaxStaleness 

func MaxStaleness(d time.Duration) TimestampBound

MaxStaleness returns a TimestampBound that will perform reads and queries at a time chosen to be at most "d" stale.

func MinReadTimestamp 

func MinReadTimestamp(t time.Time) TimestampBound

MinReadTimestamp returns a TimestampBound that bound that will perform reads and queries at a time chosen to be at least "t".

func ReadTimestamp 

func ReadTimestamp(t time.Time) TimestampBound

ReadTimestamp returns a TimestampBound that will peform reads and queries at the given time.

func StrongRead 

func StrongRead() TimestampBound

StrongRead returns a TimestampBound that will perform reads and queries at a timestamp where all previously committed transactions are visible.

func (TimestampBound) String 

func (tb TimestampBound) String() string

Source Files

View all Source files

Directories

Path Synopsis
admin
database/apiv1
Package database is an auto-generated package for the Cloud Spanner Database Admin API.
 Package database is an auto-generated package for the Cloud Spanner Database Admin API.
instance/apiv1
Package instance is an auto-generated package for the Cloud Spanner Instance Admin API.
 Package instance is an auto-generated package for the Cloud Spanner Instance Admin API.
Package spanner is an auto-generated package for the Cloud Spanner API.
 Package spanner is an auto-generated package for the Cloud Spanner API.
internal
testutil

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