datastore

package
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 Go to latest Published: Jan 18, 2016 License: Apache-2.0 Imports: 18 Imported by: 0

Documentation

Overview

Package datastore contains a Google Cloud Datastore client.

This package is experimental and may make backwards-incompatible changes.

Example (Auth)

TODO(djd): reevaluate this example given new Client config. 

package main

import (
	"io/ioutil"
	"log"

	"golang.org/x/net/context"
	"golang.org/x/oauth2/google"
	"google.golang.org/cloud"
	"google.golang.org/cloud/datastore"
)

func main() *datastore.Client {
	// Initialize an authorized context with Google Developers Console
	// JSON key. Read the google package examples to learn more about
	// different authorization flows you can use.
	// http://godoc.org/golang.org/x/oauth2/google
	jsonKey, err := ioutil.ReadFile("/path/to/json/keyfile.json")
	if err != nil {
		log.Fatal(err)
	}
	conf, err := google.JWTConfigFromJSON(
		jsonKey,
		datastore.ScopeDatastore,
		datastore.ScopeUserEmail,
	)
	if err != nil {
		log.Fatal(err)
	}
	ctx := context.Background()
	client, err := datastore.NewClient(ctx, "project-id", cloud.WithTokenSource(conf.TokenSource(ctx)))
	if err != nil {
		log.Fatal(err)
	}
	// Use the client (see other examples).
	return client
}

Output:

Index

Examples

Constants

View Source 
const (
	// ScopeDatastore grants permissions to view and/or manage datastore entities
	ScopeDatastore = "https://www.googleapis.com/auth/datastore"

	// ScopeUserEmail grants permission to view the user's email address.
	// It is required to access the datastore.
	ScopeUserEmail = "https://www.googleapis.com/auth/userinfo.email"
)

Variables

View Source 
var (
	// ErrInvalidEntityType is returned when functions like Get or Next are
	// passed a dst or src argument of invalid type.
	ErrInvalidEntityType = errors.New("datastore: invalid entity type")
	// ErrInvalidKey is returned when an invalid key is presented.
	ErrInvalidKey = errors.New("datastore: invalid key")
	// ErrNoSuchEntity is returned when no entity was found for a given key.
	ErrNoSuchEntity = errors.New("datastore: no such entity")
)
View Source 
var Done = errors.New("datastore: query has no more results")

Done is returned when a query iteration has completed.

View Source 
var ErrConcurrentTransaction = errors.New("datastore: concurrent transaction")

ErrConcurrentTransaction is returned when a transaction is rolled back due to a conflict with a concurrent transaction.

Functions

func LoadStruct 

func LoadStruct(dst interface{}, p []Property) error

LoadStruct loads the properties from p to dst. dst must be a struct pointer.

func WithNamespace 

func WithNamespace(parent context.Context, namespace string) context.Context

WithNamespace returns a new context that limits the scope its parent context with a Datastore namespace.

Types

type Client 

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

Client is a client for reading and writing data in a datastore dataset.

func NewClient 

func NewClient(ctx context.Context, projectID string, opts ...cloud.ClientOption) (*Client, error)

NewClient creates a new Client for a given dataset.

func (*Client) AllocateIDs 

func (c *Client) AllocateIDs(ctx context.Context, keys []*Key) ([]*Key, error)

AllocateIDs accepts a slice of incomplete keys and returns a slice of complete keys that are guaranteed to be valid in the datastore

func (*Client) Count 

func (c *Client) Count(ctx context.Context, q *Query) (int, error)

Count returns the number of results for the given query.

func (*Client) Delete 

func (c *Client) Delete(ctx context.Context, key *Key) error

Delete deletes the entity for the given key.

func (*Client) DeleteMulti 

func (c *Client) DeleteMulti(ctx context.Context, keys []*Key) error

DeleteMulti is a batch version of Delete.

func (*Client) Get 

func (c *Client) Get(ctx context.Context, key *Key, dst interface{}) error

Get loads the entity stored for key into dst, which must be a struct pointer or implement PropertyLoadSaver. If there is no such entity for the key, Get returns ErrNoSuchEntity.

The values of dst's unmatched struct fields are not modified, and matching slice-typed fields are not reset before appending to them. In particular, it is recommended to pass a pointer to a zero valued struct on each Get call.

ErrFieldMismatch is returned when a field is to be loaded into a different type than the one it was stored from, or when a field is missing or unexported in the destination struct. ErrFieldMismatch is only returned if dst is a struct pointer.

func (*Client) GetAll 

func (c *Client) GetAll(ctx context.Context, q *Query, dst interface{}) ([]*Key, error)

GetAll runs the provided query in the given context and returns all keys that match that query, as well as appending the values to dst.

dst must have type *[]S or *[]*S or *[]P, for some struct type S or some non- interface, non-pointer type P such that P or *P implements PropertyLoadSaver.

As a special case, *PropertyList is an invalid type for dst, even though a PropertyList is a slice of structs. It is treated as invalid to avoid being mistakenly passed when *[]PropertyList was intended.

The keys returned by GetAll will be in a 1-1 correspondence with the entities added to dst.

If q is a “keys-only” query, GetAll ignores dst and only returns the keys.

func (*Client) GetMulti 

func (c *Client) GetMulti(ctx context.Context, keys []*Key, dst interface{}) error

GetMulti is a batch version of Get.

dst must be a []S, []*S, []I or []P, for some struct type S, some interface type I, or some non-interface non-pointer type P such that P or *P implements PropertyLoadSaver. If an []I, each element must be a valid dst for Get: it must be a struct pointer or implement PropertyLoadSaver.

As a special case, PropertyList is an invalid type for dst, even though a PropertyList is a slice of structs. It is treated as invalid to avoid being mistakenly passed when []PropertyList was intended.

func (*Client) NewTransaction 

func (c *Client) NewTransaction(ctx context.Context, opts ...TransactionOption) (*Transaction, error)

NewTransaction starts a new transaction.

func (*Client) Put 

func (c *Client) Put(ctx context.Context, key *Key, src interface{}) (*Key, error)

Put saves the entity src into the datastore with key k. src must be a struct pointer or implement PropertyLoadSaver; if a struct pointer then any unexported fields of that struct will be skipped. If k is an incomplete key, the returned key will be a unique key generated by the datastore.

func (*Client) PutMulti 

func (c *Client) PutMulti(ctx context.Context, keys []*Key, src interface{}) ([]*Key, error)

PutMulti is a batch version of Put.

src must satisfy the same conditions as the dst argument to GetMulti.

func (*Client) Run 

func (c *Client) Run(ctx context.Context, q *Query) *Iterator

Run runs the given query in the given context.

func (*Client) RunInTransaction 

func (c *Client) RunInTransaction(ctx context.Context, f func(tx *Transaction) error, opts ...TransactionOption) (*Commit, error)

RunInTransaction runs f in a transaction. f is invoked with a Transaction that f should use for all the transaction's datastore operations.

f must not call Commit or Rollback on the provided Transaction.

If f returns nil, RunInTransaction commits the transaction, returning the Commit and a nil error if it succeeds. If the commit fails due to a conflicting transaction, RunInTransaction retries f with a new Transaction. It gives up and returns ErrConcurrentTransaction after three failed attempts.

If f returns non-nil, then the transaction will be rolled back and RunInTransaction will return the same error. The function f is not retried.

Note that when f returns, the transaction is not committed. Calling code must not assume that any of f's changes have been committed until RunInTransaction returns nil.

Since f may be called multiple times, f should usually be idempotent. Note that Transaction.Get is not idempotent when unmarshaling slice fields.

type Commit 

type Commit struct{}

Commit represents the result of a committed transaction.

func (*Commit) Key 

func (c *Commit) Key(p *PendingKey) *Key

Key resolves a pending key handle into a final key.

type Cursor 

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

Cursor is an iterator's position. It can be converted to and from an opaque string. A cursor can be used from different HTTP requests, but only with a query with the same kind, ancestor, filter and order constraints.

func DecodeCursor 

func DecodeCursor(s string) (Cursor, error)

Decode decodes a cursor from its base-64 string representation.

func (Cursor) String 

func (c Cursor) String() string

String returns a base-64 string representation of a cursor.

type ErrFieldMismatch 

type ErrFieldMismatch struct {
	StructType reflect.Type
	FieldName  string
	Reason     string
}

ErrFieldMismatch is returned when a field is to be loaded into a different type than the one it was stored from, or when a field is missing or unexported in the destination struct. StructType is the type of the struct pointed to by the destination argument passed to Get or to Iterator.Next.

func (*ErrFieldMismatch) Error 

func (e *ErrFieldMismatch) Error() string

type Iterator 

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

Iterator is the result of running a query.

func (*Iterator) Cursor 

func (t *Iterator) Cursor() (Cursor, error)

Cursor returns a cursor for the iterator's current location.

func (*Iterator) Next 

func (t *Iterator) Next(dst interface{}) (*Key, error)

Next returns the key of the next result. When there are no more results, Done is returned as the error.

If the query is not keys only and dst is non-nil, it also loads the entity stored for that key into the struct pointer or PropertyLoadSaver dst, with the same semantics and possible errors as for the Get function.

type Key 

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

Key represents the datastore key for a stored entity, and is immutable.

func DecodeKey 

func DecodeKey(encoded string) (*Key, error)

DecodeKey decodes a key from the opaque representation returned by Encode.

func NewIncompleteKey 

func NewIncompleteKey(ctx context.Context, kind string, parent *Key) *Key

NewIncompleteKey creates a new incomplete key. kind cannot be empty.

func NewKey 

func NewKey(ctx context.Context, kind, name string, id int64, parent *Key) *Key

NewKey creates a new key. kind cannot be empty. Either one or both of name and id must be zero. If both are zero, the key returned is incomplete. parent must either be a complete key or nil.

func (*Key) Encode 

func (k *Key) Encode() string

Encode returns an opaque representation of the key suitable for use in HTML and URLs. This is compatible with the Python and Java runtimes.

func (*Key) Equal 

func (k *Key) Equal(o *Key) bool

func (*Key) GobDecode 

func (k *Key) GobDecode(buf []byte) error

func (*Key) GobEncode 

func (k *Key) GobEncode() ([]byte, error)

func (*Key) ID 

func (k *Key) ID() int64

func (*Key) Incomplete 

func (k *Key) Incomplete() bool

Complete returns whether the key does not refer to a stored entity.

func (*Key) Kind 

func (k *Key) Kind() string

func (*Key) MarshalJSON 

func (k *Key) MarshalJSON() ([]byte, error)

func (*Key) Name 

func (k *Key) Name() string

func (*Key) Namespace 

func (k *Key) Namespace() string

func (*Key) Parent 

func (k *Key) Parent() *Key

func (*Key) SetParent 

func (k *Key) SetParent(v *Key)

func (*Key) String 

func (k *Key) String() string

String returns a string representation of the key.

func (*Key) UnmarshalJSON 

func (k *Key) UnmarshalJSON(buf []byte) error

type MultiError 

type MultiError []error

MultiError is returned by batch operations when there are errors with particular elements. Errors will be in a one-to-one correspondence with the input elements; successful elements will have a nil entry.

func (MultiError) Error 

func (m MultiError) Error() string

type PendingKey 

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

PendingKey represents the key for newly-inserted entity. It can be resolved into a Key by calling the Key method of Commit.

type Property 

type Property struct {
	// Name is the property name.
	Name string
	// Value is the property value. The valid types are:
	//	- int64
	//	- bool
	//	- string
	//	- float64
	//	- *Key
	//	- time.Time
	//	- []byte (up to 1 megabyte in length)
	// This set is smaller than the set of valid struct field types that the
	// datastore can load and save. A Property Value cannot be a slice (apart
	// from []byte); use multiple Properties instead. Also, a Value's type
	// must be explicitly on the list above; it is not sufficient for the
	// underlying type to be on that list. For example, a Value of "type
	// myInt64 int64" is invalid. Smaller-width integers and floats are also
	// invalid. Again, this is more restrictive than the set of valid struct
	// field types.
	//
	// A Value will have an opaque type when loading entities from an index,
	// such as via a projection query. Load entities into a struct instead
	// of a PropertyLoadSaver when using a projection query.
	//
	// A Value may also be the nil interface value; this is equivalent to
	// Python's None but not directly representable by a Go struct. Loading
	// a nil-valued property into a struct will set that field to the zero
	// value.
	Value interface{}
	// NoIndex is whether the datastore cannot index this property.
	// If NoIndex is set to false, []byte values are limited to 1500 bytes and
	// string values are limited to 1500 bytes.
	NoIndex bool
	// Multiple is whether the entity can have multiple properties with
	// the same name. Even if a particular instance only has one property with
	// a certain name, Multiple should be true if a struct would best represent
	// it as a field of type []T instead of type T.
	Multiple bool
}

Property is a name/value pair plus some metadata. A datastore entity's contents are loaded and saved as a sequence of Properties. An entity can have multiple Properties with the same name, provided that p.Multiple is true on all of that entity's Properties with that name.

func SaveStruct 

func SaveStruct(src interface{}) ([]Property, error)

SaveStruct returns the properties from src as a slice of Properties. src must be a struct pointer.

type PropertyList 

type PropertyList []Property

PropertyList converts a []Property to implement PropertyLoadSaver.

func (*PropertyList) Load 

func (l *PropertyList) Load(p []Property) error

Load loads all of the provided properties into l. It does not first reset *l to an empty slice.

func (*PropertyList) Save 

func (l *PropertyList) Save() ([]Property, error)

Save saves all of l's properties as a slice of Properties.

type PropertyLoadSaver 

type PropertyLoadSaver interface {
	Load([]Property) error
	Save() ([]Property, error)
}

PropertyLoadSaver can be converted from and to a slice of Properties.

type Query 

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

Query represents a datastore query.

Example 
package main

import (
	"log"
	"time"

	"golang.org/x/net/context"
	"google.golang.org/cloud/datastore"
)

func main() {
	ctx := context.Background()
	client, err := datastore.NewClient(ctx, "project-id")
	if err != nil {
		log.Fatal(err)
	}

	// Count the number of the post entities.
	q := datastore.NewQuery("Post")
	n, err := client.Count(ctx, q)
	if err != nil {
		log.Fatal(err)
	}
	log.Println("There are %d posts.", n)

	// List the posts published since yesterday.
	yesterday := time.Now().Add(-24 * time.Hour)
	q = datastore.NewQuery("Post").Filter("PublishedAt >", yesterday)
	it := client.Run(ctx, q)
	// Use the iterator.
	_ = it

	// Order the posts by the number of comments they have recieved.
	datastore.NewQuery("Post").Order("-Comments")

	// Start listing from an offset and limit the results.
	datastore.NewQuery("Post").Offset(20).Limit(10)
}

Output:

func NewQuery 

func NewQuery(kind string) *Query

NewQuery creates a new Query for a specific entity kind.

An empty kind means to return all entities, including entities created and managed by other App Engine features, and is called a kindless query. Kindless queries cannot include filters or sort orders on property values.

func (*Query) Ancestor 

func (q *Query) Ancestor(ancestor *Key) *Query

Ancestor returns a derivative query with an ancestor filter. The ancestor should not be nil.

func (*Query) Distinct 

func (q *Query) Distinct() *Query

Distinct returns a derivative query that yields de-duplicated entities with respect to the set of projected fields. It is only used for projection queries.

func (*Query) End 

func (q *Query) End(c Cursor) *Query

End returns a derivative query with the given end point.

func (*Query) EventualConsistency 

func (q *Query) EventualConsistency() *Query

EventualConsistency returns a derivative query that returns eventually consistent results. It only has an effect on ancestor queries.

func (*Query) Filter 

func (q *Query) Filter(filterStr string, value interface{}) *Query

Filter returns a derivative query with a field-based filter. The filterStr argument must be a field name followed by optional space, followed by an operator, one of ">", "<", ">=", "<=", or "=". Fields are compared against the provided value using the operator. Multiple filters are AND'ed together. Field names which contain spaces, quote marks, or operator characters should be passed as quoted Go string literals as returned by strconv.Quote or the fmt package's %q verb.

func (*Query) KeysOnly 

func (q *Query) KeysOnly() *Query

KeysOnly returns a derivative query that yields only keys, not keys and entities. It cannot be used with projection queries.

func (*Query) Limit 

func (q *Query) Limit(limit int) *Query

Limit returns a derivative query that has a limit on the number of results returned. A negative value means unlimited.

func (*Query) Offset 

func (q *Query) Offset(offset int) *Query

Offset returns a derivative query that has an offset of how many keys to skip over before returning results. A negative value is invalid.

func (*Query) Order 

func (q *Query) Order(fieldName string) *Query

Order returns a derivative query with a field-based sort order. Orders are applied in the order they are added. The default order is ascending; to sort in descending order prefix the fieldName with a minus sign (-). Field names which contain spaces, quote marks, or the minus sign should be passed as quoted Go string literals as returned by strconv.Quote or the fmt package's %q verb.

func (*Query) Project 

func (q *Query) Project(fieldNames ...string) *Query

Project returns a derivative query that yields only the given fields. It cannot be used with KeysOnly.

func (*Query) Start 

func (q *Query) Start(c Cursor) *Query

Start returns a derivative query with the given start point.

func (*Query) Transaction 

func (q *Query) Transaction(t *Transaction) *Query

Transaction returns a derivative query that is associated with the given transaction.

All reads performed as part of the transaction will come from a single consistent snapshot. Furthermore, if the transaction is set to a serializable isolation level, another transaction cannot concurrently modify the data that is read or modified by this transaction.

type Transaction 

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

Transaction represents a set of datastore operations to be committed atomically.

Operations are enqueued by calling the Put and Delete methods on Transaction (or their Multi-equivalents). These operations are only committed when the Commit method is invoked. To ensure consistency, reads must be performed by using Transaction's Get method or by using the Transaction method when building a query.

A Transaction must be committed or rolled back exactly once.

Example 
package main

import (
	"log"

	"golang.org/x/net/context"
	"google.golang.org/cloud/datastore"
)

func main() {
	ctx := context.Background()
	client, err := datastore.NewClient(ctx, "project-id")
	if err != nil {
		log.Fatal(err)
	}
	const retries = 3

	// Increment a counter.
	// See https://cloud.google.com/appengine/articles/sharding_counters for
	// a more scalable solution.
	type Counter struct {
		Count int
	}

	key := datastore.NewKey(ctx, "counter", "CounterA", 0, nil)

	for i := 0; i < retries; i++ {
		tx, err := client.NewTransaction(ctx)
		if err != nil {
			break
		}

		var c Counter
		if err := tx.Get(key, &c); err != nil && err != datastore.ErrNoSuchEntity {
			break
		}
		c.Count++
		if _, err := tx.Put(key, &c); err != nil {
			break
		}

		// Attempt to commit the transaction. If there's a conflict, try again.
		if _, err := tx.Commit(); err != datastore.ErrConcurrentTransaction {
			break
		}
	}

}

Output:

func (*Transaction) Commit 

func (t *Transaction) Commit() (*Commit, error)

Commit applies the enqueued operations atomically.

func (*Transaction) Delete 

func (t *Transaction) Delete(key *Key) error

Delete is the transaction-specific version of the package function Delete. Delete enqueues the deletion of the entity for the given key, to be committed atomically upon calling Commit.

func (*Transaction) DeleteMulti 

func (t *Transaction) DeleteMulti(keys []*Key) error

DeleteMulti is a batch version of Delete.

func (*Transaction) Get 

func (t *Transaction) Get(key *Key, dst interface{}) error

Get is the transaction-specific version of the package function Get. All reads performed during the transaction will come from a single consistent snapshot. Furthermore, if the transaction is set to a serializable isolation level, another transaction cannot concurrently modify the data that is read or modified by this transaction.

func (*Transaction) GetMulti 

func (t *Transaction) GetMulti(keys []*Key, dst interface{}) error

GetMulti is a batch version of Get.

func (*Transaction) Put 

func (t *Transaction) Put(key *Key, src interface{}) (*PendingKey, error)

Put is the transaction-specific version of the package function Put.

Put returns a PendingKey which can be resolved into a Key using the return value from a successful Commit. If key is an incomplete key, the returned pending key will resolve to a unique key generated by the datastore.

func (*Transaction) PutMulti 

func (t *Transaction) PutMulti(keys []*Key, src interface{}) ([]*PendingKey, error)

PutMulti is a batch version of Put. One PendingKey is returned for each element of src in the same order.

func (*Transaction) Rollback 

func (t *Transaction) Rollback() error

Rollback abandons a pending transaction.

type TransactionOption 

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

A TransactionOption configures the Transaction returned by NewTransaction. 

var (
	// Snapshot causes the transaction to enforce a snapshot isolation level.
	Snapshot TransactionOption = isolation{pb.BeginTransactionRequest_SNAPSHOT}
	// Serializable causes the transaction to enforce a serializable isolation level.
	Serializable TransactionOption = isolation{pb.BeginTransactionRequest_SERIALIZABLE}
)

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