如何在PlayFramework中的Json Reads中添加自定义ValidationError

Question

I am using play Reads validation helpers i want to show some custom message in case of json exception eg:length is minimum then specified or the given email is not valid , i knnow play displays the error message like this error.minLength but i want to display a reasonable message like please enter the character greater then 1 (or something ) here is my code

case class DirectUserSignUpValidation(firstName: String,
                                      lastName: String,
                                      email: String,
                                      password: String) extends Serializable

object DirectUserSignUpValidation {
  var validationErrorMsg=""
  implicit val readDirectUser: Reads[DirectUserSignUpValidation] = (
  (JsPath \ "firstName").read(minLength[String](1)) and
    (JsPath \ "lastName").read(minLength[String](1)) and
    (JsPath \ "email").read(email) and
    (JsPath \ "password").read(minLength[String](8).
      filterNot(ValidationError("Password is all numbers"))(_.forall(_.isDigit)).
      filterNot(ValidationError("Password is all letters"))(_.forall(_.isLetter))
    )) (UserSignUpValidation.apply _)
}

i have tried to add ValidationError like this

 (JsPath \ "email").read(email,Seq(ValidationError("email address not correct")) and
   but its giving me compile time error


  too many arguments for method read: (t: T)play.api.libs.json.Reads[T]

please helo how can i add custom validationError messages while reading json data

Answer 1

There is no such thing as (JsPath \\ "firstName").read(minLength[String](1)) in play json. what you can do with custom error message is this:

(JsPath \ "firstName").read[String].filter(ValidationError("your.error.message"))(_.length > 0)

Answer 2

ValidationError messages are supposed to be keys to be used for translation, not human readable messages.

However, if you still want to change the message for minLength , you'll need to reimplement it, since it is hard-coded.

Thankfully, the source code is available, so you can easily change it as you please:

def minLength[M](m: Int)(implicit reads: Reads[M], p: M => scala.collection.TraversableLike[_, M]) =
  filterNot[M](JsonValidationError("error.minLength", m))(_.size < m)

If you want to use a more generic pattern to specify errors, the only access you have is using the result from your validation. For instance, you could do

val json: JsValue = ???
json.validate[DirectUserSignUpValidation] match {
  case JsSuccess(dusuv, _) => doSomethingWith(dusuv)
  case JsError(errs) => doSomethingWithErrors(errs)
}

Or, with a more compact approach

json.validate[DirectUserSignUpValidation].
  fold(doSomethingWithErrors, doSomethingWith)