Question

我尝试定义trait Required来封装逻辑以验证所需Record Field的存在，但是，我还没有能够弄清楚自我类型应该是什么。我的目标是能够尽可能地写出一些东西，例如object foo extends SomeField(...) with Required但是我确实意识到我可能必须明确地将一些类型参数传递给Required。

到目前为止我的无能为力是：

import net.liftweb.record.Field import net.liftweb.util.FieldError

trait Required[ThisType, OwnerType] {
  this: Field[ThisType, OwnerType] =>
  def errMsg = "is required"

  override def validations = {
    val required =
      (x: String) => if (x.isEmpty) List(FieldError(this, errMsg)) else Nil
    // this asInstanceOf call also seems fishy
    // --why's it even required if we already have the self type in place?
    required :: super.asInstanceOf[Field[ThisType, OwnerType]].validations
  }
}

但是，这会导致与存在类型相关的编译错误和警告：

myfield = object SomeField(...) with Required[SomeField[SomeModel], SomeModel]

就简明with Required而言，更不用说了。

修改

我提出了这个问题：

trait Required[OwnerType] extends Field[String, OwnerType] {
  def errMsg = "is required"

  override def validations = {
    val required =
      (x: String) => if (x.isEmpty) List(FieldError(this, errMsg)) else Nil
    required :: super.validations
  }
}

但是，它不允许我将required添加到super.validations，因为它期望this.type.ValueType => List[FieldError]不是String => List[FieldError]，我觉得这很奇怪，因为在Field[String, ...]，ValueType String。

如果我将required更改为ValueType => ...，则会进行编译，但会出现with Required[SomeModel]错误：

类型参数[String，OwnerType]不符合trait Field的类型参数边界[ThisType，OwnerType＆lt ;:net.liftweb.record.Record [OwnerType]]

...即使StringField.ThisType是String而String.OwnerType是Record[SomeModel]的子类，SomeModel是MongoRecord[SomeModel]的子类。 - 我输了。

P.S。这与Lift Record: empty value for required field but no validation errors

有关

Answer 1

以下在SBT控制台中编译。

import net.liftweb.util._
import net.liftweb.record._
import net.liftweb.record.field._

trait Required extends StringTypedField {

  override def validations: List[ValidationFunction] = valMinLen(1, "Required!") _ :: super.validations

}

class TestRecord extends Record[TestRecord] {

    val meta = TestRecord

    object testField extends StringField(this, 255) with Required

}

object TestRecord extends TestRecord with MetaRecord[TestRecord]

具有Lift中的特征的通用字段验证

1 个答案: