Overview

In this tutorial, we will explore two libraries that can be used to validate the field of a struct in Golang. The two libraries are

• gopkg.in/go-playground/validator.v9 – https://pkg.go.dev/github.com/go-playground/validator

• github.com/asaskevich/govalidator – https://github.com/asaskevich/govalidator

For this tutorial, we will use the below employee struct

type employee struct {
    Name string
}

First Library (go-playground/validator)

Let’s first see the playground validator library. Below is the code for the same.

go.mod

module sample.com/validate
go 1.14
require (
    github.com/go-playground/universal-translator v0.17.0 // indirect
    github.com/leodido/go-urn v1.2.1 // indirect
    gopkg.in/go-playground/assert.v1 v1.2.1 // indirect
    gopkg.in/go-playground/validator.v9 v9.31.0
)

main.go

package main
import (
    "fmt"
    "gopkg.in/go-playground/validator.v9"
)

var validate *validator.Validate

type employee struct {
    Name string `validate:"required"`
}

func main() {
    e := employee{}
    err := validateStruct(e)
    if err != nil {
        fmt.Printf("Error: %s\n", err)
    }
}

func validateStruct(e employee) error {
    validate = validator.New()
    err := validate.Struct(e)
    if err != nil {
        return err
    }
    return nil
}

Output

Error: Key: 'employee.Name' Error:Field validation for 'Name' failed on the 'required' tag

First, we need to declare the instance of Validate

var validate *validator.Validate

Notice here that we need to associate meta tags with fields of the struct to let the validator know that you want to validate this field. In the above example, we added the tag with the Name field. This tag is interpreted by the playground validate library.

type employee struct {
    Name string `validate:"required"`
}

Then call the Struct method to validate the struct

validate.Struct(e)

It raises the correct error as we have passed the Name field as nil

Second Library (asaskevich/govalidator)

go.mod

module sample.com/validator
go 1.14

require github.com/asaskevich/govalidator v0.0.0-20200907205600-7a23bdc65eef

main.go

package main

import (
	"fmt"

	"github.com/asaskevich/govalidator"
)

type employee struct {
	Name string `valid:"required"`
}

func main() {
	e := employee{}
	err := validateStruct(e)
	if err != nil {
		fmt.Printf("Error: %s\n", err)
	}
}

func validateStruct(e employee) error {
	_, err := govalidator.ValidateStruct(e)
	if err != nil {
		return err
	}
	return nil

}

Output

Error: Name: non zero value required

Similar to the above example we associated tags with the Name field which govalidator can interpret

Name string `valid:"required"`

Then we call the ValidateStruct function and it raises the correct error as we have passed the Name field as nil