Form input Validation in Revel

Question

Im learning Revel and using the Validation package to do some checks on input. I want to see if there already exists a record with a "name" in DB (i get a input from user through a form) and if true return error else create a record. Im am able to validate (with built in methods like Required, Maxlen ...) a field and display the error in HTML. But for my custom check Is adding a custom Validator to the Validation package the way to go or is there a way i can add custom keys and error to the Validation Context. I couldnt find how i can added custom keys and message to the error map. Thanks.

Answer 1

revel's validators.Validator interface looks like this:

type Validator interface {
    IsSatisfied(interface{}) bool
    DefaultMessage() string
}

And *validation.Validation has a method:

func (v *Validation) Check(obj interface{}, checks ...Validator) *ValidationResult

And *validation.ValidationResult has a method:

func (*ValidationResult) Message

Putting that all together:

type usernameChecker struct {}

func(u usernameChecker) IsSatisified(i interface{}) bool {
    s, k := i.(string)

    if !k {
        return false
    }

    /* check if s exists in DB */
}

func(u usernameChecker) DefaultMessage() string {
    return "username already in use"
}

And in your application:

func (c MyApp) SaveUser(username string) revel.Result {
    c.Validation.Check(username, usernameChecker{}).Message("more specific or translated message in case of failure")
}

This is one if not the most badly designed validation library I have ever seen.