Using validator package to validate struct fields in Golang

Validating fields in a struct is a frequent case in daily development, fortunately, Golang has provided an excellent package named validator to help us accomplish this task. At first, we download the validator:

go get gopkg.in/go-playground/validator.v9

Assume that we need to validate every user that's entering our website now, we can do as such:

package main

import (
	"fmt"

	"gopkg.in/go-playground/validator.v9"
)

type User struct {
	Name     string `json:"firstname" validate:"required"`
	Address  string `json:"lastname" validate:"omitempty"`
	Age      string `json:"username" validate:"required,gte=18"`
	Password string `json:"password" validate:"required,gte=8"`
}

func main() {
	user := User{
		Name:    "tom",
		Address: "Beijing, district chaoyang",
	}
	validate := validator.New()
	err := validate.Struct(user)
	if err != nil {
		fmt.Println(err)
		return
	}
	fmt.Println("Success")
}

The code above will generate output as follows:

Key: 'User.Age' Error:Field validation for 'Age' failed on the 'required' tag
Key: 'User.Password' Error:Field validation for 'Password' failed on the 'required' tag

If we change the user value to satisfy the validate tag defined in User Struct,

user := User{
		Name:     "tom",
		Address:  "Beijing, district chaoyang",
		Age:      20,
		Password: "0123456789",
	}

Then we can get the output:

Success

All of the tags that can be used can be found in this page: pkg.go.dev/github.com/…