使用 Scala Cats Validated 验证多个 ADT

Question

我正在尝试验证 scala 中的配置。首先，我将配置 json 转换为相应的案例类，然后验证它。因为我想慢慢失败，所以我收集所有失败的验证，而不是在第一次验证失败后返回。我打算使用猫库Cats validation提供的应用函子。

我面临的问题是链接中显示的表单验证适用于简单案例类

final case class RegistrationData(username: String, password: String, firstName: String, lastName: String, age: Int)

// Below is the code snippet for applying validation from the link   itself
 {
(validateUserName(username),
validatePassword(password),
validateFirstName(firstName),
validateLastName(lastName),
validateAge(age)).mapN(RegistrationData)}

// A more complex case for validations
final case class User(name:String,adds:List[Addresses])
final case class Address(street:String,lds:List[LandMark])
final case class LandMark(wellKnown:Boolean,street:String)

在这种情况下，字段“用户名”的验证独立于“名字”的验证。但是如果

1. 我不得不对“firstName”和“userName”进行某种类型的验证（假设 Levenstein 距离应该是
2. case 类不是由简单的原语 (Int,String) 组成，而是有其他 case 类作为其成员。例如上面提到的用户案例类。

一般来说，应用函子的方法适合这种情况吗？我什至应该收集所有失败的验证吗？

PS：如果提到不正确的地方，请原谅我，我是 scala 的新手。

Answer 1

基于猫的验证示例

import cats.data._
import cats.data.Validated._
import cats.implicits._

final case class RegistrationData(name: Name, age: Int, workAge: Int)

final case class Name(firstName: String, lastName: String)

sealed trait DomainValidation {
  def errorMessage: String
}

case object FirstNameHasSpecialCharacters extends DomainValidation {
  def errorMessage: String =
    "First name cannot contain spaces, numbers or special characters."
}

case object LastNameHasSpecialCharacters extends DomainValidation {
  def errorMessage: String =
    "Last name cannot contain spaces, numbers or special characters."
}

case object AgeIsInvalid extends DomainValidation {
  def errorMessage: String =
    "You must be aged 18 and not older than 75 to use our services."
}

case object AgeIsLessThanWorkInvalid extends DomainValidation {
  def errorMessage: String =
    "You must be aged 18 and not older than 75 to use our services."
}

sealed trait FormValidatorNec {

  type ValidationResult[A] = ValidatedNec[DomainValidation, A]

  private def validateFirstName(firstName: String): ValidationResult[String] =
    if (firstName.matches("^[a-zA-Z]+$")) firstName.validNec
    else FirstNameHasSpecialCharacters.invalidNec

  private def validateLastName(lastName: String): ValidationResult[String] =
    if (lastName.matches("^[a-zA-Z]+$")) lastName.validNec
    else LastNameHasSpecialCharacters.invalidNec

  private def validateAge(age: Int,
                          workAge: Int): ValidationResult[(Int, Int)] = {
    if (age >= 18 && age <= 75 && workAge >= 0)
      if (age > workAge)
        (age, workAge).validNec
      else
        AgeIsLessThanWorkInvalid.invalidNec
    else
      AgeIsInvalid.invalidNec
  }

  def validateForm(firstName: String,
                   lastName: String,
                   age: Int,
                   workAge: Int): ValidationResult[RegistrationData] = {
    (
      (validateFirstName(firstName), validateLastName(lastName)).mapN(Name),
      validateAge(age, workAge)
    ).mapN {
      case (n, (a, w)) => RegistrationData(name = n, age = a, workAge = w)
    }
  }

}

object FormValidatorNec extends FormValidatorNec

println(FormValidatorNec.validateForm("firstname", "lastname", 40, 30))
println(FormValidatorNec.validateForm("firs2tname", "lastname", 20, 30))

查看fiddle

只有当元组(ValidationResult[_], ValidationResult[_], ...)中的数据为Valid时，才会调用mapN的函数。如果元组中的一个或多个元素是Invalid，则将它们收集到NotEmtpyChain 中。

总之，所有validate方法都被调用，当所有方法都返回Valid[_]时，mapN函数被应用。