Getting the correct field name on bind validation errors

[OranShuster]

Description

When gettig an error back from ShouldBind* methods, im looking for a way to return to the user the correct field names
Looking at the ValidationErrors and FieldError structs i don't see the actual name of the query param
Is this a validator limitation or can this be solved by gin?

Side note - this part of the gin documentation is a bit lacking. it would be very beneficial to add an example about using ValidationErrors , instead of just a normal go error, when binding

How to reproduce

package main

import (
	"errors"
	"net/http"

	"github.com/gin-gonic/gin"
	"github.com/go-playground/validator/v10"
)

type queryTestStruct struct {
	Param1 string `form:"othername" binding:"required"`
}

func main() {
	r := gin.Default()
	r.GET("/testQuery", func(c *gin.Context) {
		var params queryTestStruct
		err := c.ShouldBindQuery(&params)
		if err != nil {
			var ve validator.ValidationErrors
			if errors.As(err, &ve) {
				out := map[string]interface{}{}
				for _, fe := range ve {
					fieldName := fe.Field()
					error := fe.Error()
					out[fieldName] = error
				}
				c.AbortWithStatusJSON(http.StatusBadRequest, gin.H{"errors": out})
			}
			return
		}
		c.JSON(200, "No error")
	})
	r.Run() // listen and serve on 0.0.0.0:8080 (for windows "localhost:8080")
}

Expectations

I expect to have some way to get from the FieldError struct the actual expected query param name: othername

Actual result

$ curl --location 'localhost:8080/testQuery'
{
    "errors": {
        "Param1": "Key: 'queryTestStruct.Param1' Error:Field validation for 'Param1' failed on the 'required' tag"
    }
}

Environment

• go version: 1.23
• gin version (or commit ref): v1.10.0
• operating system: Windows 11

[jerryyummy]

you do not include the parameter, should use :curl -G "http://localhost:8080/testQuery" --data-urlencode "othername=your_value"

[OranShuster]

you do not include the parameter, should use :curl -G "http://localhost:8080/testQuery" --data-urlencode "othername=your_value"

you are misunderstanding my question, im talking about query parameters error handling. obviously if ill send the parameter i won't get any error

[GenJi77JYXC]

Maybe you can solve this problem using reflection

Here are some of my solutions

package main

import (
	"errors"
	"fmt"
	"github.com/go-playground/validator/v10"
	"net/http"
	"reflect"

	"github.com/gin-gonic/gin"
)

type queryTestStruct struct {
	Param1 string `form:"othername" binding:"required"`
}

func main() {
	r := gin.Default()
	r.GET("/testQuery", func(c *gin.Context) {
		var params queryTestStruct
		err := c.ShouldBindQuery(&params)
		if err != nil {
			rType := reflect.TypeOf(new(queryTestStruct)).Elem()
			
			var ve validator.ValidationErrors
			if errors.As(err, &ve) {
				out := map[string]interface{}{}
				for _, fe := range ve {
					fieldName := fe.Field()
					param, ok := rType.FieldByName(fieldName)
					if ok {
						fmt.Println(param.Tag.Get("form"))//  // Get param's correct field name
					}
					error := fe.Error()
					out[fieldName] = error
					out["tagName"] = param.Tag.Get("form")
				}
				c.AbortWithStatusJSON(http.StatusBadRequest, gin.H{"errors": out})
			}
			return
		}
		c.JSON(200, "No error")
	})
	r.Run() // listen and serve on 0.0.0.0:8080 (for windows "localhost:8080")
}

Actual result

curl : {"errors":{"Param1":"Key: 'queryTestStruct.Param1' Error:Field validation for 'Param1' failed on the 'required' tag","tagName":"othername"}}

I used the tagName field to return the information you want

[jakubtomany]

That's great there is a workaround with reflection, however, it would be great if gin binding package handles it correctly by registering a TagNameFunc as mentioned here: go-playground/validator#681 (comment)