Option columns and condition folding

[Mike Limansky]

Hi all,

   I'm trying to use Slick 3.1.1 in my current project and I've faced with following problem. I have schema with optional fields:

 

class Foos(tag: Tag) extends Table[Foo](tag, "foos") {
  def id = column[Long]("id", O.PrimaryKey, O.AutoInc)
  def a = column[Option[String]]("a")
  def b = column[String]("b")

  // and some more fields, both optional and not
}

In a service class I have optional parameters, since some of them can be not defined. I'm trying to reduce conditions to one query, like it shown in the Slick documentation, but it doesn't compile:

def findFoos(a: Option[String], b: Option[String]) = { // and some more parameters here

  val query = (f: Foos) => List(
    a.map(f.a === _),
    b.map(f.b === _)
  ).flatten.reduceLeftOption(_ && _).getOrElse(true: Rep[Boolean])

The problem, this cannot be folded. As I understand the reason is that items have different types: Rep[Boolean] for not nullable fields and Rep[Option[Boolean]] for optionals. How should I use it properly?

--
Regards,
Mike.

[Naftoli Gugenheim]

On Mon, Mar 28, 2016, 10:25 AM Mike Limansky <mike.l...@gmail.com> wrote:

Hi all,

   I'm trying to use Slick 3.1.1 in my current project and I've faced with following problem. I have schema with optional fields:

 

class Foos(tag: Tag) extends Table[Foo](tag, "foos") {
  def id = column[Long]("id", O.PrimaryKey, O.AutoInc)
  def a = column[Option[String]]("a")
  def b = column[String]("b")

  // and some more fields, both optional and not
}

In a service class I have optional parameters, since some of them can be not defined. I'm trying to reduce conditions to one query, like it shown in the Slick documentation, but it doesn't compile:

Does it tell you why it doesn't compile?

def findFoos(a: Option[String], b: Option[String]) = { // and some more parameters here

  val query = (f: Foos) => List(
    a.map(f.a === _),
    b.map(f.b === _)
  ).flatten.reduceLeftOption(_ && _).getOrElse(true: Rep[Boolean])

The problem, this cannot be folded. As I understand the reason is that items have different types: Rep[Boolean] for not nullable fields and Rep[Option[Boolean]] for optionals. How should I use it properly?

--
Regards,
Mike.

--

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[Mike Limansky]

The error is following:

[error] projects/test/src/main/scala/Service.scala:42: value && is not a member of slick.lifted.Rep[_201]
[error]     ).flatten.reduceLeftOption(_ && _).getOrElse(true: Rep[_])
[error]                                  ^
[error] one error found

I think that since the list contains both Rep[Boolean] and Rep[Option[Boolean]] the type of the list will be List[Rep[Any]] (IntelliJ Idea shows it like List[Rep[_ >: Option[Boolean] with Boolean]]. As result neither booleanColumnExtensionMethods nor booleanOptionColumnExtensionMethods implicit methods doesn't applies to the list values.

I just wondering if there any common solution for such situation. The only idea I have now is to create two separate lists for optional and non-optional fields and merge it by hands, but it looks little bit ugly for me.

вторник, 29 марта 2016 г., 7:41:55 UTC+3 пользователь nafg написал:

[Naftoli Gugenheim]

First write it out concrete, then see how you can pull out and abstract over the repetitiveness. In this case I believe that might involve a polymorphic (having a type parameter) function. But in order to identify what your can do, let's see how it looks written out concrete and repetitive.

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