Bind should support default values

[atedja]

Bind() is great, but what do you guys think if it supports default values when a param is not specified? Something like this:

    params = struct {
        Name string `form:"name,default=john"`
        Age uint `form:"address,default=10"`
    }{}

    c.Bind(&param)

[thinkerou]

Hi @atedja I have commit one pull request and I attempt to complete it.

[thinkerou]

@atedja Now the pr have merged to the master branch.

[appleboy]

Implement in #1138 . try it in the latest master branch.

[calixwu]

So, how to use it???

[KingJeason]

So, how to use it ???

[to2false]

@KingJeason @calixwu

`form:"field_name,default=value"`

It worked for me.

[calixwu]

@to2false I have already used it that way, but thanks all the same. I think it's better to document this usage.

[SnowOnion]

Another story. For those who, like me, want default JSON field value when using BindJSON:
Just set the default value when initializing the struct. E.g.

params = struct {
	Name string `json:"name"`
	Age  uint   `json:"address"`
}{
	Name: "john",
	Age:  10,
}
c.BindJSON(&params)

And from this issue I got to know anonymous struct.

I learnt a lot today.

[Gera-coder]

Another story. For those who, like me, want default JSON field value when using BindJSON:
Just set the default value when initializing the struct. E.g.

params = struct {
	Name string `json:"name"`
	Age  uint   `json:"address"`
}{
	Name: "john",
	Age:  10,
}
c.BindJSON(&params)

And from this issue I got to know anonymous struct.

I learnt a lot today.

Hi Snow, I tried your way but it can only work with field missing.
For example, if you passed in a json string with age set to init value zero, 10 would got replaced.

[kamly]

@thinkerou @SnowOnion @Gera-coder

I want to wirte this

type Param struct {
   Name string `json:"name,default=john"`
   Age uint `json:"address,default=10"`
}
var param Param
c.ShouldBind(&param)

but it doesn't work, has any good method in ShouldBind JSON?

[runzhliu]

I think the default value doesn't work for the json type, actually, I find no related unitest for the default value except for the form type, but assigning the default value before the binding works for me.

[kangour]

if use dive then default invalid, help.

[olivatooo]

help 😔

[AuroraTea]

@KingJeason @calixwu

`form:"field_name,default=value"`

It worked for me.

Sorry for Interrupting you, is it now discarded?

type ReqListUsers struct {
	Limit  int64  `form:"limit,default=20" binding:"min=1,max=100"`
	Sort   string `form:"sort,default=id" binding:"omitempty,oneof=id createAt lastLoginAt"`
	Order  string `form:"order,default=asc" binding:"omitempty,oneof=asc desc"`
}

func ListUsers(c *gin.Context) {
	var req ReqListUsers
	err := c.ShouldBindQuery(&req)

But not work.

[hexuan1922]

@thinkerou @SnowOnion @Gera-coder

I want to wirte this

type Param struct {
   Name string `json:"name,default=john"`
   Age uint `json:"address,default=10"`
}
var param Param
c.ShouldBind(&param)

but it doesn't work, has any good method in ShouldBind JSON?

type User struct {
	Name string `form:"name,default=user1" json:"name,default=user2"`
	Age  int    `form:"age,default=10" json:"age,default=20"`
}

r := gin.Default()

// way1 curl 127.0.0.1:8900/bind?name=aa
// way2 curl -X POST 127.0.0.1:8900/bind -d "name=aa&age=30"
// way3 curl -X POST 127.0.0.1:8900/bind -H "Content-Type: application/json" -d "{\"name\": \"aa\"}"
r.Any("/bind", func(c *gin.Context) {
    var user User
    //user = User{Name: "bb", Age: 11} //way4:A variable of type User can be generated with the default value before bind

    if c.ContentType() == binding.MIMEJSON {
        //way5:A variable of type User can be generated with the default value before bind.
        _ = binding.MapFormWithTag(&user, nil, "json")
    }

    _ = c.Bind(&user) //Note that because bind is used here to request json, you specify the Content-Type header
    c.String(200, "Hello %v age %v", user.Name, user.Age)
})

// The above 4 way.
// way1/2 structTag is work.because gin at queryBinding/formBinding execute mapFormByTag logic, will check formTag
// way3 structTag not work. gin at jsonBinding non-execution  mapFormByTag logic
// way4/way5 no matter query/form/json All valid
// way5 is work.  Because the mapFormByTag logic is triggered in addition

r.Run(":8900")

good luck. @kamly