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Published: Oct 21, 2015 License: BSD-3-Clause, GPL-2.0 Imports: 7 Imported by: 0



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Package gorilla/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 Load() 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 a 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:

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

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

	<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">

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 registry a converter, like:

type Person struct {
  Emails []Email

type Email struct {

func (e *Email) UnmarshalText(text []byte) (err error) {
	e.Address, err = mail.ParseAddress(string(text))
} HTML form that accepts three Email values would look like this:

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



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type ConversionError

type ConversionError struct {
	Key   string // key from the source map.
	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 custome 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 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

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