schema

Documentation

Overview

Package schema fills a struct with form values.

The basic usage is really simple. Given this struct:

type Person struct {
	Name  string
	Phone string
}

...we can fill it passing a map to the Decode() function:

values := map[string][]string{
	"Name":  {"John"},
	"Phone": {"999-999-999"},
}
person := new(Person)
decoder := schema.NewDecoder()
decoder.Decode(person, values)

This is just a simple example and it doesn't make a lot of sense to create the map manually. Typically it will come from a http.Request object and will be of type url.Values, http.Request.Form, or http.Request.MultipartForm:

func MyHandler(w http.ResponseWriter, r *http.Request) {
	err := r.ParseForm()

	if err != nil {
		// Handle error
	}

	decoder := schema.NewDecoder()
	// r.PostForm is a map of our POST form values
	err := decoder.Decode(person, r.PostForm)

	if err != nil {
		// Handle error
	}

	// Do something with person.Name or person.Phone
}

Note: it is a good idea to set a Decoder instance as a package global, because it caches meta-data about structs, and an instance can be shared safely:

var decoder = schema.NewDecoder()

To define custom names for fields, use a struct tag "schema". To not populate certain fields, use a dash for the name and it will be ignored:

type Person struct {
	Name  string `schema:"name"`  // custom name
	Phone string `schema:"phone"` // custom name
	Admin bool   `schema:"-"`     // this field is never set
}

The supported field types in the destination struct are:

• bool
• float variants (float32, float64)
• int variants (int, int8, int16, int32, int64)
• string
• uint variants (uint, uint8, uint16, uint32, uint64)
• struct
• a pointer to one of the above types
• a slice or a pointer to a slice of one of the above types

Non-supported types are simply ignored, however custom types can be registered to be converted.

To fill nested structs, keys must use a dotted notation as the "path" for the field. So for example, to fill the struct Person below:

type Phone struct {
	Label  string
	Number string
}

type Person struct {
	Name  string
	Phone Phone
}

...the source map must have the keys "Name", "Phone.Label" and "Phone.Number". This means that an HTML form to fill a Person struct must look like this:

<form>
	<input type="text" name="Name">
	<input type="text" name="Phone.Label">
	<input type="text" name="Phone.Number">
</form>

Single values are filled using the first value for a key from the source map. Slices are filled using all values for a key from the source map. So to fill a Person with multiple Phone values, like:

type Person struct {
	Name   string
	Phones []Phone
}

...an HTML form that accepts three Phone values would look like this:

<form>
	<input type="text" name="Name">
	<input type="text" name="Phones.0.Label">
	<input type="text" name="Phones.0.Number">
	<input type="text" name="Phones.1.Label">
	<input type="text" name="Phones.1.Number">
	<input type="text" name="Phones.2.Label">
	<input type="text" name="Phones.2.Number">
</form>

Notice that only for slices of structs the slice index is required. This is needed for disambiguation: if the nested struct also had a slice field, we could not translate multiple values to it if we did not use an index for the parent struct.

There's also the possibility to create a custom type that implements the TextUnmarshaler interface, and in this case there's no need to register a converter, like:

type Person struct {
  Emails []Email
}

type Email struct {
  *mail.Address
}

func (e *Email) UnmarshalText(text []byte) (err error) {
	e.Address, err = mail.ParseAddress(string(text))
	return
}

...an HTML form that accepts three Email values would look like this:

<form>
	<input type="email" name="Emails.0">
	<input type="email" name="Emails.1">
	<input type="email" name="Emails.2">
</form>

Index

• type ConversionError
  • func (e ConversionError) Error() string
• type Converter
• type Decoder
  • func NewDecoder() *Decoder
  • func (d *Decoder) Decode(dst interface{}, src map[string][]string) error
  • func (d *Decoder) IgnoreUnknownKeys(i bool)
  • func (d *Decoder) RegisterConverter(value interface{}, converterFunc Converter)
  • func (d *Decoder) SetAliasTag(tag string)
  • func (d *Decoder) ZeroEmpty(z bool)
• type EmptyFieldError
  • func (e EmptyFieldError) Error() string
• type Encoder
  • func NewEncoder() *Encoder
  • func (e *Encoder) Encode(src interface{}, dst map[string][]string) error
  • func (e *Encoder) RegisterEncoder(value interface{}, encoder func(reflect.Value) string)
  • func (e *Encoder) SetAliasTag(tag string)
• type MultiError
  • func (e MultiError) Error() string
• type UnknownKeyError
  • func (e UnknownKeyError) Error() string

Types

type ConversionError

type ConversionError struct {
	Key   string       // key from the source map.
	Type  reflect.Type // expected type of elem
	Index int          // index for multi-value fields; -1 for single-value fields.
	Err   error        // low-level error (when it exists)
}

ConversionError stores information about a failed conversion.

func (ConversionError) Error

func (e ConversionError) Error() string

type Converter

type Converter func(string) reflect.Value

type Decoder

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

Decoder decodes values from a map[string][]string to a struct.

func NewDecoder

func NewDecoder() *Decoder

NewDecoder returns a new Decoder.

func (*Decoder) Decode

func (d *Decoder) Decode(dst interface{}, src map[string][]string) error

Decode decodes a map[string][]string to a struct.

The first parameter must be a pointer to a struct.

The second parameter is a map, typically url.Values from an HTTP request. Keys are "paths" in dotted notation to the struct fields and nested structs.

See the package documentation for a full explanation of the mechanics.

func (*Decoder) IgnoreUnknownKeys

func (d *Decoder) IgnoreUnknownKeys(i bool)

IgnoreUnknownKeys controls the behaviour when the decoder encounters unknown keys in the map. If i is true and an unknown field is encountered, it is ignored. This is similar to how unknown keys are handled by encoding/json. If i is false then Decode will return an error. Note that any valid keys will still be decoded in to the target struct.

To preserve backwards compatibility, the default value is false.

func (*Decoder) RegisterConverter

func (d *Decoder) RegisterConverter(value interface{}, converterFunc Converter)

RegisterConverter registers a converter function for a custom type.

func (*Decoder) SetAliasTag

func (d *Decoder) SetAliasTag(tag string)

SetAliasTag changes the tag used to locate custom field aliases. The default tag is "schema".

func (*Decoder) ZeroEmpty

func (d *Decoder) ZeroEmpty(z bool)

ZeroEmpty controls the behaviour when the decoder encounters empty values in a map. If z is true and a key in the map has the empty string as a value then the corresponding struct field is set to the zero value. If z is false then empty strings are ignored.

The default value is false, that is empty values do not change the value of the struct field.

type EmptyFieldError

type EmptyFieldError struct {
	Key string // required key in the source map.
}

EmptyFieldError stores information about an empty required field.

func (EmptyFieldError) Error

func (e EmptyFieldError) Error() string

type Encoder

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

Encoder encodes values from a struct into url.Values.

func NewEncoder

func NewEncoder() *Encoder

NewEncoder returns a new Encoder with defaults.

func (*Encoder) Encode

func (e *Encoder) Encode(src interface{}, dst map[string][]string) error

Encode encodes a struct into map[string][]string.

Intended for use with url.Values.

func (*Encoder) RegisterEncoder

func (e *Encoder) RegisterEncoder(value interface{}, encoder func(reflect.Value) string)

RegisterEncoder registers a converter for encoding a custom type.

func (*Encoder) SetAliasTag

func (e *Encoder) SetAliasTag(tag string)

SetAliasTag changes the tag used to locate custom field aliases. The default tag is "schema".

type MultiError

type MultiError map[string]error

MultiError stores multiple decoding errors.

Borrowed from the App Engine SDK.

func (MultiError) Error

func (e MultiError) Error() string

type UnknownKeyError

type UnknownKeyError struct {
	Key string // key from the source map.
}

UnknownKeyError stores information about an unknown key in the source map.

func (UnknownKeyError) Error

func (e UnknownKeyError) Error() string