使用 Shapeless 将 Map[String,Any] 转换为 case 类 [英] Converting Map[String,Any] to a case class using Shapeless

问题描述

问题此处询问关于映射case 类到 Map[String,Any].我想知道相反的方法是什么，将 Map[String,Any] 转换为 case 类.鉴于以下地图:

The question here asks about mapping a case class to a Map[String,Any]. I was wondering what would be the other way around, converting Map[String,Any] to a case class. Given the following map:

val mp = Map("name" -> "Tom", "address" -> Map("street" -> "Jefferson st", "zip" -> 10000))

将其转换为Person的case类:

Convert it to a case class of Person:

case class Person(name:String, address:Address)
case class Address(street:String, zip:Int)

val p = Person("Tom", Address("Jefferson st", 10000))

像这样:

val newP = mp.asCC[Person]
assert(newP.get == p)

我应该如何使用 Shapeless 做到这一点.

How should I do that with Shapeless.

推荐答案

这是一个现成的、大部分未经测试的解决方案.首先是类型类:

Here's an off-the-cuff, mostly untested solution. First for the type class:

import shapeless._, labelled.{ FieldType, field }

trait FromMap[L <: HList] {
  def apply(m: Map[String, Any]): Option[L]
}

然后是实例:

trait LowPriorityFromMap {
  implicit def hconsFromMap1[K <: Symbol, V, T <: HList](implicit
    witness: Witness.Aux[K],
    typeable: Typeable[V],
    fromMapT: Lazy[FromMap[T]]
  ): FromMap[FieldType[K, V] :: T] = new FromMap[FieldType[K, V] :: T] {
    def apply(m: Map[String, Any]): Option[FieldType[K, V] :: T] = for {
      v <- m.get(witness.value.name)
      h <- typeable.cast(v)
      t <- fromMapT.value(m)
    } yield field[K](h) :: t
  }
}

object FromMap extends LowPriorityFromMap {
  implicit val hnilFromMap: FromMap[HNil] = new FromMap[HNil] {
    def apply(m: Map[String, Any]): Option[HNil] = Some(HNil)
  }

  implicit def hconsFromMap0[K <: Symbol, V, R <: HList, T <: HList](implicit
    witness: Witness.Aux[K],
    gen: LabelledGeneric.Aux[V, R],
    fromMapH: FromMap[R],
    fromMapT: FromMap[T]
  ): FromMap[FieldType[K, V] :: T] = new FromMap[FieldType[K, V] :: T] {
    def apply(m: Map[String, Any]): Option[FieldType[K, V] :: T] = for {
      v <- m.get(witness.value.name)
      r <- Typeable[Map[String, Any]].cast(v)
      h <- fromMapH(r)
      t <- fromMapT(m)
    } yield field[K](gen.from(h)) :: t
  }
}

为了方便起见，还有一个辅助类:

And then a helper class for convenience:

class ConvertHelper[A] {
  def from[R <: HList](m: Map[String, Any])(implicit
    gen: LabelledGeneric.Aux[A, R],
    fromMap: FromMap[R]
  ): Option[A] = fromMap(m).map(gen.from(_))
}

def to[A]: ConvertHelper[A] = new ConvertHelper[A]

示例:

case class Address(street: String, zip: Int)
case class Person(name: String, address: Address)

val mp = Map(
  "name" -> "Tom",
  "address" -> Map("street" -> "Jefferson st", "zip" -> 10000)
)

最后:

scala> to[Person].from(mp)
res0: Option[Person] = Some(Person(Tom,Address(Jefferson st,10000)))

这仅适用于成员为 Typeable 的 case 类或成员为 Typeable 或其他 case 类的其他 case 类......(等等).

This will only work for case classes whose members are either Typeable or other case classes whose members are either Typeable or other case classes… (and so on).

注意不要在导入中使用 scala.reflect.runtime.universe._，因为这会破坏上述内容.

Careful not to have scala.reflect.runtime.universe._ in your imports, as this will break the above.

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