Revel parameter binding

Revel makes it as easy as possible for parameters from the client to be converted to data types in the Go language. This conversion from string to another type is called "data binding."

Parameters

All request parameters are collected into a Params object. Including:

• URL path parameters
• URL query parameters
• Form field (Multipart or not)
• File upload

Params objects are defined in ( godoc ):

type Params struct {
    url.Values
    Files map[string][]*multipart.FileHeader
}

Embedded url.Values (godoc) provides query support for simple values, but developers can more easily use Revel's data binding support to extract parameters to any data type.

Controller method parameter binding

Parameters can be bound directly to controller methods, such as:

func (c AppController) Action(name string, ids []int, user User, img []byte) revel.Result {
    ...
}

Before the controller method is executed, Revel resolves the argument to the specified data type through the variable name biner, and if the resolution parameter fails, the parameter is parsed to the initial value of the target data type.

The binder

Use Revel's binder to bind a parameter to the specified data type (godoc), which integrates the Params object. For example:

func (c SomeController) Action() revel.Result {
    var ids []int
    c.Params.Bind(&ids, "ids")
    ...
}

The types of data supported are:

• Int
• Bool
• Point
• Slice
• Struct
• time. Time
• File upload: sos. F ile, []byte, io. R eader, io. ReadSeeker

The syntax of data type binding is described below, and the detailed description can also refer to the source code.

Booleans

The strings "true," "on," and "1" are bound to true, while the others are false .

Slices

Slice binding has two syntaxes: ordered and out of order

Ordered:

?ids[0]=1
&ids[1]=2
&ids[3]=4

The binding result []int{1, 2, 0, 4}

Disordered:

?ids[]=1
&ids[]=2
&ids[]=3

The binding result []int{1, 2, 3}

Note: Only ordered slices can be bound to a struct:

?user[0].Id=1
&user[0].Name=rob
&user[1].Id=2
&user[1].Name=jenny

Struct

Struct simply uses a . To bind:

?user.Id=1
&user.Name=rob
&user.Friends[]=2
&user.Friends[]=3
&user.Father.Id=5
&user.Father.Name=Hermes

Binding to the following struct type:

type User struct {
    Id int
    Name string
    Friends []int
    Father User
}

Note: The fields in struct must be exported (capital letters).

Date / Time

Built-in SQL Standard Time Format ("2006-01-02", "2006-01-02 15:04")

Use Revel Official Mode to simply add a time format to the TimeFormats variable:

func init() {
    revel.TimeFormats = append(revel.TimeFormats, "01/02/2006")
}

File upload

File upload parameters can be bound to the following types:

• *os. File
• []byte
• Io. Reader
• Io. ReadSeeker

It's a wrapper for Go's multipart package. The file is kept in memory, and if the file size exceeds 10MB (the default), it is saved to a temporary file.

Note: Binding os.File type, which is saved to a temporary file (if not), is inefficient.

Custom biner

The application can define biners.

The custom binder needs to implement the binder interface and register the custom type:

var myBinder = revel.Binder{
    Bind: func(params *revel.Params, name string, typ reflect.Type) reflect.Value {...},
    Unbind: func(output map[string]string, name string, val interface{}) {...},
}

func init() {
    revel.TypeBinders[reflect.TypeOf(MyType{})] = myBinder