使用 Shapeless 将 Map[String,Any] 转换为 case class

Question

问题询问有关将案例 class 映射到 Map[String,Any] 的问题。我想知道反过来会怎样，将 Map[String,Any] 转换为 case class。给定以下地图：

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

将其转换为 Person 的 class 大小写：

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。

Answer 1

这是一个现成的、大部分未经测试的解决方案。首先是类型 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，还有一个助手class：

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]

以及示例：

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 class 或成员为 Typeable 或其他 case [=34] 的其他 case classes =]是的……（依此类推）。

陷阱

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

使用 Shapeless 将 Map[String,Any] 转换为 case class

Converting Map[String,Any] to a case class using Shapeless

scala

shapeless

陷阱