使用Argonaut进行Scalaz验证 [英] Scalaz validation with Argonaut

问题描述

我有一个案例类和一个伴随对象:

I have a case class and companion object:

case class Person private(name: String, age: Int)

object Person {

  def validAge(age: Int) = {
    if (age > 18) age.successNel else "Age is under 18".failureNel
  }

  def validName(name: String) = {
    name.successNel
  }

  def create(name: String, age: Int) = (validAge(age) |@| validName(name))(Person.apply)

}

我想使用Argonaut解析一些JSON并返回一个Person或一些错误，作为一个列表.所以我需要:

I want to use Argonaut to parse some JSON and return a Person OR some errors, as a list. So I need to:

1. 从字符串中读取JSON，并验证字符串格式正确
2. 将JSON解码为Person或错误字符串列表.

我想以某种形式返回错误，我可以将其转换为更多的JSON，例如:

I want to return errors in the form of something I can turn into some more JSON like:

{
  errors: ["Error1", "Error2"]
}

我首先尝试使用Argonauts的解码验证方法，该方法返回Validation [String，X].不幸的是，我需要一个错误列表.

I first tried using Argonauts decodeValidation method, which returns a Validation[String, X]. Unfortunately, I need a List of errors.

有什么建议吗?

推荐答案

我将其添加为答案，因为这是我从头开始解决问题的方法，但我一直没有密切注意与Argonaut一起开发了一段时间，我很想听听有更好的方法.首先进行设置，它可以解决您的一些小问题，并为名称添加有效条件，以使后面的示例更加有趣:

I'm adding this as an answer because it's how I'd solve the problem off the top of my head, but I haven't been keeping up closely with Argonaut development for a while, and I'd love to hear that there's a better way. First for the setup, which fixes a few little issues in yours, and adds a condition for validity on names to make the examples later more interesting:

import scalaz._, Scalaz._

case class Person private(name: String, age: Int)

object Person {
  def validAge(age: Int): ValidationNel[String, Int] =
    if (age > 18) age.successNel else "Age is under 18".failureNel

  def validName(name: String): ValidationNel[String, String] =
    if (name.size >= 3) name.successNel else "Name too short".failureNel

  def create(name: String, age: Int) =
    (validName(name) |@| validAge(age))(Person.apply)
}

然后在创建Person之前将JSON解码为(String, Int)对:

And then I'd decode the JSON into a (String, Int) pair before creating the Person:

import argonaut._, Argonaut._

def decodePerson(in: String): ValidationNel[String, Person] =
  Parse.decodeValidation(in)(
    jdecode2L((a: String, b: Int) => (a, b)
  )("name", "age")).toValidationNel.flatMap {
    case (name, age) => Person.create(name, age)
  }

然后:

scala> println(decodePerson("""{ "name": "", "age": 1 }"""))
Failure(NonEmptyList(Name too short, Age is under 18))

请注意，这不会在更复杂的情况下(例如，如果name字段的值是一个数字，而age是1，则只会得到一个错误(name一个).在这种情况下使错误累积有效得多.

Note that this doesn't accumulate errors in more complex cases—e.g. if the value of the name field is a number and age is 1, you'll only get a single error (the name one). Making error accumulation work in cases like that would be considerably more complex.

相关地，您还将在Validation上看到有关flatMap的弃用警告，您可以将其视为提醒，说明绑定期间不会发生累积.您可以通过导入scalaz.Validation.FlatMap._告诉编译器您了解.

Relatedly, you'll also see a deprecation warning about the flatMap on Validation, which you can think of as a reminder that accumulation won't happen across the bind. You can tell the compiler that you understand by importing scalaz.Validation.FlatMap._.

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