allow ignoring field on form mapping

[bazaglia]

As discussed in issue #610 when using c.Bind(), sometimes we don't want to bind certain fields from the user request. While this can be done adding json:"-" to field tag, the same can't be achieved for multipart/formdata requests.

This PR allows setting in the tag form:"-", which solves the described issue.

[codecov]

Codecov Report

Merging #1733 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1733      +/-   ##
==========================================
+ Coverage   98.48%   98.48%   +<.01%     
==========================================
  Files          41       41              
  Lines        2047     2049       +2     
==========================================
+ Hits         2016     2018       +2     
  Misses         19       19              
  Partials       12       12

Impacted Files	Coverage Δ
binding/form_mapping.go	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4e86b17...11afd07. Read the comment docs.

[thinkerou]

not json:"-" but binding:"-" which also can use for multipart/formdata, thanks!

type LoginForm struct {
	User     string `form:"user" binding:"required"`
	Password string `form:"password" binding:"-"`
}

func main() {
	router := gin.Default()
	router.POST("/login", func(c *gin.Context) {
		var form LoginForm
		if c.Bind(&form) == nil {
			c.JSON(200, gin.H{"msg:": form.User + " " + form.Password})
		}
	})
	router.Run(":8080")
}

curl -v --form user=user --form password=password http://localhost:8080/login
curl -v --form user=user --form password1=password http://localhost:8080/login

[bazaglia]

@thinkerou hey, thanks for your comment.

problem is, as my comment here #610 (comment), gin uses binding for validation. That means the field still decoded by c.Bind even when setting binding:"-". That was I added form:"-", that's corresponding to json:"-", but for forms.

In your example, when printing form.Password, it won't return a nil pointer (<nil>), but a memory address (like 0xc00001e510 that points to an empty string). This is really anoying specifically when saving data to a SQL database (it will save an empty string, not null)

[hotcoffie]

its not working properly now. When I added form:"-" to my field, the field is still being assigned a value regardless of whether I use Bind or ShouldBind.

type Astruct struct {
	Aa string  `form:"-" json:"aa"`
	Bb *string `form:"-" json:"bb"`
}

func Init(r *gin.Engine) {

	api := r.Group("/api")
	{
		api.GET("/ping", func(c *gin.Context) {
			c.JSON(http.StatusOK, "pong")
		})

		api.POST("/test", func(ctx *gin.Context) {
			var a Astruct
			ctx.Bind(&a)
			fmt.Println(a.Aa)
			fmt.Println(*a.Bb)
			ctx.AbortWithStatus(http.StatusOK)
		})
	}
}

POST http://127.0.0.1:9527/api/test
Content-Type: application/json

{
	"aa": "a",
	"bb": "b"
}

a
b
2023-09-05T01:30:16.577+0800	DEBUG	utils/logger.go:43	gin	{"method": "POST", "path": "/api/test", "status": 200, "ip": "127.0.0.1", "elapsed": "243.845µs"}