请关注我，在OP有意义之前有一些背景。我使用Slick 3.1.x和光滑的代码生成器。 btw整个源代码可以在play-authenticate-usage-scala github project中找到。对于这个项目，我希望有一个光滑的通用Dao，以避免为每个模型重复相同的样板代码。
我有一个postgres sql脚本，使用evolutions创建数据库： 1.sql
然后我调用生成以下数据模型的生成器： Tables.scala
为了能够为模型类提供通用的dao slick实现，我需要它们遵守一些基本的抽象，例如。
id例如需要dao的findById def copyWithNewId(id : PK) : Entity[PK]。这是dao的createAndFetch实现所需要的，该实现持久保存新实体并在一个步骤中检索自动生成的id PK。 此copyWithNewId是OP的要点。请注意，它被称为copyWithNewId而不是copy，以避免无限递归。为了能够实现允许插入并立即获取自动生成的id的{{3}}，实体行需要来自copy(id = id)案例类的<Model>Row方法。它的定义GenericDaoAutoIncImpl尚不清楚。相关实施如下：
override def createAndFetch(entity: E): Future[Option[E]] = {
val insertQuery = tableQuery returning tableQuery.map(_.id)
into ((row, id) => row.copyWithNewId(id))
db.run((insertQuery += entity).flatMap(row => findById(row.id)))
}
这要求我在每个copyWithNewId AutoInc生成的模型中实施id方法，这样做并不好。
// generated code and modified later to adapt it for the generic dao
case class UserRow(id: Long, ...) extends AutoIncEntity[Long] with Subject {
override def copyWithNewId(id : Long) : Entity[Long] = this.copy(id = id)
}
但是，如果我可以 - 使用一些Scala技巧 - 定义我的<Model>Row案例类Base类的子类，它是可复制的并且除了传递的id之外自己复制。对IdCopyable copy(id = id) {}进行copyWithNewId，我不需要为每个<Model>Row生成的案例类一遍又一遍地实施copy(id = id)。
有没有办法抽象或＆＃34;拉起＆＃34;对于包含id属性的任何案例类，重构scala> abstract class BaseA[A <: BaseA[_]] { def copy(id : Int) : A }
defined class BaseA
scala> case class A(id: Int) extends BaseA[A]
<console>:12: error: class A needs to be abstract, since method copy in class BaseA of type (id: Int)A is not defined
case class A(id: Int) extends BaseA[A]
^
scala> case class A(id: Int); val a = A(5); a.copy(6)
defined class A
a: A = A(5)
res0: A = A(6)
？还有其他推荐的解决方案吗？
更新1 以下几乎总结了我遇到的问题：
[error] /home/bravegag/code/play-authenticate-usage-scala/app/dao/GenericDaoAutoIncImpl.scala:26: could not find implicit value for parameter gen: shapeless.Generic.Aux[E,Repr]
[error] val insertQuery = tableQuery returning tableQuery.map(_.id) into ((row, id) => row.copyWithNewId(id))
[error] ^
[error] /home/bravegag/code/play-authenticate-usage-scala/app/dao/GenericDaoAutoIncImpl.scala:27: value id is not a member of insertQuery.SingleInsertResult
[error] db.run((insertQuery += entity).flatMap(row => findById(row.id)))
[error] ^
[error] two errors found
更新2 使用下面提出的解决方案，我收到以下编译错误：
import shapeless._, tag.@@
import shapeless._
import tag.$at$at
/**
* Identifyable base for all Strong Entity Model types
* @tparam PK Primary key type
* @tparam E Actual case class EntityRow type
*/
trait AutoIncEntity[PK, E <: AutoIncEntity[PK, E]] extends Entity[PK] { self: E =>
//------------------------------------------------------------------------
// public
//------------------------------------------------------------------------
/**
* Returns the entity with updated id as generated by the database
* @param id The entity id
* @return the entity with updated id as generated by the database
*/
def copyWithNewId(id : PK)(implicit mkLens: MkFieldLens.Aux[E, Symbol @@ Witness.`"id"`.T, PK]) : E = {
(lens[E] >> 'id).set(self)(id)
}
}
更新3 使用和调整下面提出的镜头解决方案我得到以下编译器错误：
[error] /home/bravegag/code/play-authenticate-usage-scala/app/dao/GenericDaoAutoIncImpl.scala:26: could not find implicit value for parameter mkLens: shapeless.MkFieldLens.Aux[E,shapeless.tag.@@[Symbol,String("id")],PK]
[error] val insertQuery = tableQuery returning tableQuery.map(_.id) into ((row, id) => row.copyWithNewId(id))
[error] ^
[error] /home/bravegag/code/play-authenticate-usage-scala/app/dao/GenericDaoAutoIncImpl.scala:27: value id is not a member of insertQuery.SingleInsertResult
[error] db.run((insertQuery += entity).flatMap(row => findById(row.id)))
[error] ^
然后我得到以下编译器错误：
[2016-12-06T12:04:49] NOTE: started server, waiting for clients
[2016-12-06T12:04:49] DEBUG: event queue is ready
[2016-12-06T12:04:49] DEBUG: add pending events to buffer
[2016-12-06T12:04:49] DEBUG: screen "Ian-PC" shape changed
[2016-12-06T12:04:49] DEBUG: accepted ipc client connection
[2016-12-06T12:04:49] DEBUG: start ipc handle data
[2016-12-06T12:04:49] DEBUG: ipc read: IHEL
[2016-12-06T12:04:49] DEBUG: finished ipc handle data
[2016-12-06T12:04:49] DEBUG: ipc hello, type=node
[2016-12-06T12:04:49] INFO: watchdog status: ok
[2016-12-06T12:04:50] DEBUG: started process, session=1, elevated: yes, command="C:/Program Files (x86)/Synergy/synergys.exe" -f --no-tray --debug DEBUG --name Ian-PC --ipc --enable-drag-drop --profile-dir "C:\Users\Ian\AppData\Local" -c "C:/Users/Ian/AppData/Local/Temp/qt_temp.ZU7304" --address :24800 --serial-key MY_LICENCE_KEY --res-w 1920 --res-h 1080 --prm-wc 960 --prm-hc 540
[2016-12-06T12:04:55] INFO: zeroconf client detected: Ian-Mac.local
答案 0 :(得分：9)
使用shapeless，您可以抽象出案例类。
如果假设每个id都是Long并且是案例类的第一个参数，它可能如下所示：
scala> import shapeless._, ops.hlist.{IsHCons, Prepend}
import shapeless._
import ops.hlist.{IsHCons, Prepend}
scala> trait Copy[A <: Copy[A]] { self: A =>
| def copyWithId[Repr <: HList, Tail <: HList](l: Long)(
| implicit
| gen: Generic.Aux[A,Repr],
| cons: IsHCons.Aux[Repr,Long,Tail],
| prep: Prepend.Aux[Long :: HNil,Tail,Repr]
| ) = gen.from(prep(l :: HNil, cons.tail(gen.to(self))))
| }
defined trait Copy
scala> case class Foo(id: Long, s: String) extends Copy[Foo]
defined class Foo
scala> Foo(4L, "foo").copyWithId(5L)
res1: Foo = Foo(5,foo)
也可能以更清洁的方式;我还没有非常精通无形编程。而且我非常确定它也可以在参数列表中的任何位置使用任何类型id的案例类。 见下文第2段。
您可能希望将此逻辑封装在可重用的类型类中：
scala> :paste
// Entering paste mode (ctrl-D to finish)
import shapeless._, ops.hlist.{IsHCons, Prepend}
sealed trait IdCopy[A] {
def copyWithId(self: A, id: Long): A
}
object IdCopy {
def apply[A: IdCopy] = implicitly[IdCopy[A]]
implicit def mkIdCopy[A, Repr <: HList, Tail <: HList](
implicit
gen: Generic.Aux[A,Repr],
cons: IsHCons.Aux[Repr,Long,Tail],
prep: Prepend.Aux[Long :: HNil,Tail,Repr]
): IdCopy[A] =
new IdCopy[A] {
def copyWithId(self: A, id: Long): A =
gen.from(prep(id :: HNil, cons.tail(gen.to(self))))
}
}
// Exiting paste mode, now interpreting.
import shapeless._
import ops.hlist.{IsHCons, Prepend}
defined trait IdCopy
defined object IdCopy
scala> def copy[A: IdCopy](a: A, id: Long) = IdCopy[A].copyWithId(a, id)
copy: [A](a: A, id: Long)(implicit evidence$1: IdCopy[A])A
scala> case class Foo(id: Long, str: String)
defined class Foo
scala> copy(Foo(4L, "foo"), 5L)
res0: Foo = Foo(5,foo)
您仍然可以将copyWithId方法放在您的案例类可以扩展的特征中，如果这对您很重要：
scala> trait Copy[A <: Copy[A]] { self: A =>
| def copyWithId(id: Long)(implicit copy: IdCopy[A]) = copy.copyWithId(self, id)
| }
defined trait Copy
scala> case class Foo(id: Long, str: String) extends Copy[Foo]
defined class Foo
scala> Foo(4L, "foo").copyWithId(5L)
res1: Foo = Foo(5,foo)
重要的是，通过使用上下文边界或隐式参数，将类型类实例从使用站点传播到需要它的位置。
override def createAndFetch(entity: E)(implicit copy: IdCopy[E]): Future[Option[E]] = {
val insertQuery = tableQuery returning tableQuery.map(_.id)
into ((row, id) => row.copyWithId(id))
db.run((insertQuery += entity).flatMap(row => findById(row.id)))
}
Shapeless还提供了lenses，您可以将其用于此目的。这样，您就可以更新任何包含id字段的案例类的id字段。
scala> :paste
// Entering paste mode (ctrl-D to finish)
sealed trait IdCopy[A,ID] {
def copyWithId(self: A, id: ID): A
}
object IdCopy {
import shapeless._, tag.@@
implicit def mkIdCopy[A, ID](
implicit
mkLens: MkFieldLens.Aux[A, Symbol @@ Witness.`"id"`.T, ID]
): IdCopy[A,ID] =
new IdCopy[A,ID] {
def copyWithId(self: A, id: ID): A =
(lens[A] >> 'id).set(self)(id)
}
}
def copyWithId[ID, A](a: A, elem: ID)(implicit copy: IdCopy[A,ID]) = copy.copyWithId(a, elem)
// Exiting paste mode, now interpreting.
defined trait IdCopy
defined object IdCopy
copyWithId: [ID, A](a: A, elem: ID)(implicit copy: IdCopy[A,ID])A
scala> trait Entity[ID] { def id: ID }
defined trait Entity
scala> case class Foo(id: String) extends Entity[String]
defined class Foo
scala> def assignNewIds[ID, A <: Entity[ID]](entities: List[A], ids: List[ID])(implicit copy: IdCopy[A,ID]): List[A] =
| entities.zip(ids).map{ case (entity, id) => copyWithId(entity, id) }
assignNewIds: [ID, A <: Entity[ID]](entities: List[A], ids: List[ID])(implicit copy: IdCopy[A,ID])List[A]
scala> assignNewIds( List(Foo("foo"),Foo("bar")), List("new1", "new2"))
res0: List[Foo] = List(Foo(new1), Foo(new2))
请注意，在使用assignNewIds的方法copyWithId中，如何请求类型类IdCopy[A,ID]的实例作为隐式参数。这是因为copyWithId要求IdCopy[A,ID]的隐式实例在使用时在范围内。您需要从使用站点传播隐式实例，在这里使用具体类型（如Foo），一直到调用链的调用copyWithId。
您可以将隐式参数视为方法的依赖关系。如果方法具有类型为IdCopy[A,ID]的隐式参数，则在调用它时需要满足该依赖关系。通常，这也会对调用它的方法产生相同的依赖性。