Custom Validators

It is also possible to register custom validators. See the example code.

  1. package main
  3. import (
  4.     "net/http"
  5.     "reflect"
  6.     "time"
  8.     "github.com/gin-gonic/gin"
  9.     "github.com/gin-gonic/gin/binding"
  10.     "gopkg.in/go-playground/validator.v8"
  11. )
  13. type Booking struct {
  14.     CheckIn  time.Time `form:"check_in" binding:"required,bookabledate" time_format:"2006-01-02"`
  15.     CheckOut time.Time `form:"check_out" binding:"required,gtfield=CheckIn" time_format:"2006-01-02"`
  16. }
  18. func bookableDate(
  19.     v *validator.Validate, topStruct reflect.Value, currentStructOrField reflect.Value,
  20.     field reflect.Value, fieldType reflect.Type, fieldKind reflect.Kind, param string,
  21. ) bool {
  22.     if date, ok := field.Interface().(time.Time); ok {
  23.         today := time.Now()
  24.         if today.Year() > date.Year() || today.YearDay() > date.YearDay() {
  25.             return false
  26.         }
  27.     }
  28.     return true
  29. }
  31. func main() {
  32.     route := gin.Default()
  34.     if v, ok := binding.Validator.Engine().(*validator.Validate); ok {
  35.         v.RegisterValidation("bookabledate", bookableDate)
  36.     }
  38.     route.GET("/bookable", getBookable)
  39.     route.Run(":8085")
  40. }
  42. func getBookable(c *gin.Context) {
  43.     var b Booking
  44.     if err := c.ShouldBindWith(&b, binding.Query); err == nil {
  45.         c.JSON(http.StatusOK, gin.H{"message": "Booking dates are valid!"})
  46.     } else {
  47.         c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
  48.     }
  49. }
  1. $ curl "localhost:8085/bookable?check_in=2018-04-16&check_out=2018-04-17"
  2. {"message":"Booking dates are valid!"}
  4. $ curl "localhost:8085/bookable?check_in=2018-03-08&check_out=2018-03-09"
  5. {"error":"Key: 'Booking.CheckIn' Error:Field validation for 'CheckIn' failed on the 'bookabledate' tag"}

Struct level validations can also be registed this way.
See the struct-lvl-validation example to learn more.