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// Package main shows the validator(latest, version 9) integration with Iris.
// You can find more examples like this at:
package main
import (
// $ go get
// User contains user information.
type User struct {
FirstName string `json:"fname"`
LastName string `json:"lname"`
Age uint8 `json:"age" validate:"gte=0,lte=130"`
Email string `json:"email" validate:"required,email"`
FavouriteColor string `json:"favColor" validate:"hexcolor|rgb|rgba"`
Addresses []*Address `json:"addresses" validate:"required,dive,required"` // a person can have a home and cottage...
// Address houses a users address information.
type Address struct {
Street string `json:"street" validate:"required"`
City string `json:"city" validate:"required"`
Planet string `json:"planet" validate:"required"`
Phone string `json:"phone" validate:"required"`
// Use a single instance of Validate, it caches struct info.
var validate *validator.Validate
func main() {
validate = validator.New()
// Register validation for 'User'
// NOTE: only have to register a non-pointer type for 'User', validator
// internally dereferences during it's type checks.
validate.RegisterStructValidation(UserStructLevelValidation, User{})
app := iris.New()
app.Post("/user", func(ctx iris.Context) {
var user User
if err := ctx.ReadJSON(&user); err != nil {
// Handle error.
// Returns InvalidValidationError for bad validation input, nil or ValidationErrors ( []FieldError )
err := validate.Struct(user)
if err != nil {
// This check is only needed when your code could produce
// an invalid value for validation such as interface with nil
// value most including myself do not usually have code like this.
if _, ok := err.(*validator.InvalidValidationError); ok {
for _, err := range err.(validator.ValidationErrors) {
fmt.Println(err.StructNamespace()) // Can differ when a custom TagNameFunc is registered or.
fmt.Println(err.StructField()) // By passing alt name to ReportError like below.
// Or collect these as json objects
// and send back to the client the collected errors via ctx.JSON
// {
// "namespace": err.Namespace(),
// "field": err.Field(),
// "struct_namespace": err.StructNamespace(),
// "struct_field": err.StructField(),
// "tag": err.Tag(),
// "actual_tag": err.ActualTag(),
// "kind": err.Kind().String(),
// "type": err.Type().String(),
// "value": fmt.Sprintf("%v", err.Value()),
// "param": err.Param(),
// }
// from here you can create your own error messages in whatever language you wish.
// save user to database.
// use Postman or whatever to do a POST request
// to the http://localhost:8080/user with RAW BODY:
"fname": "",
"lname": "",
"age": 45,
"email": "",
"favColor": "#000",
"addresses": [{
"street": "Eavesdown Docks",
"planet": "Persphone",
"phone": "none",
"city": "Unknown"
// Content-Type to application/json (optionally but good practise).
// This request will fail due to the empty `User.FirstName` (fname in json)
// and `User.LastName` (lname in json).
// Check your iris' application terminal output.
app.Run(iris.Addr(":8080"), iris.WithoutServerError(iris.ErrServerClosed))
// UserStructLevelValidation contains custom struct level validations that don't always
// make sense at the field validation level. For Example this function validates that either
// FirstName or LastName exist; could have done that with a custom field validation but then
// would have had to add it to both fields duplicating the logic + overhead, this way it's
// only validated once.
// NOTE: you may ask why wouldn't I just do this outside of validator, because doing this way
// hooks right into validator and you can combine with validation tags and still have a
// common error output format.
func UserStructLevelValidation(sl validator.StructLevel) {
user := sl.Current().Interface().(User)
if len(user.FirstName) == 0 && len(user.LastName) == 0 {
sl.ReportError(user.FirstName, "FirstName", "fname", "fnameorlname", "")
sl.ReportError(user.LastName, "LastName", "lname", "fnameorlname", "")
// plus can to more, even with different tag than "fnameorlname".
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