package main import ( "database/sql" "database/sql/driver" "fmt" "reflect" "gopkg.in/bluesuncorp/validator.v6" ) // DbBackedUser User struct type DbBackedUser struct { Name sql.NullString `validate:"required"` Age sql.NullInt64 `validate:"required"` } func main() { config := validator.Config{ TagName: "validate", ValidationFuncs: validator.BakedInValidators, } validate := validator.New(config) // register all sql.Null* types to use the ValidateValuer CustomTypeFunc validate.RegisterCustomTypeFunc(ValidateValuer, sql.NullString{}, sql.NullInt64{}, sql.NullBool{}, sql.NullFloat64{}) x := DbBackedUser{Name: sql.NullString{String: "", Valid: true}, Age: sql.NullInt64{Int64: 0, Valid: false}} errs := validate.Struct(x) if len(errs) > 0 { fmt.Printf("Errs:\n%+v\n", errs) } } // ValidateValuer implements validator.CustomTypeFunc func ValidateValuer(field reflect.Value) interface{} { if valuer, ok := field.Interface().(driver.Valuer); ok { val, err := valuer.Value() if err == nil { return val } // handle the error how you want } return nil }