CODEWITHSUNDEEP
scalascalaquery
Bill
Bill

Reputation: 45476

How can I compose queries in ScalaQuery in order to create reusable traits?

I'm having some trouble composing different query components into a single Query. My goal is to create a set of traits (e.g. SoftDeletable, HasName, SortedByName, WithTimestamps) that I can simply mix-in to Table objects to add that behavior.

The ideal would look like:

abstract class BaseModel[Tuple <: Product,CaseClass](tableName: String)
     extends Table[Tuple](tableName) {
  def id = column[Int]("id", O.AutoInc, O.PrimaryKey)

  def mapped: MappedProjection[CaseClass, TupleClass]

  def allQuery = this.map(_.mapped)
  final def all = database.withSession { implicit session: Session => 
    allQuery.list() 
  }

  ...
}

trait SoftDeletable[Tuple  <: Product, CaseClass]
    extends BaseModel[Tuple,CaseClass] {
  def isActive = column[String]("is_active")

  def * = super.* ~ isActive
  def allQuery = /* here, I'd like to compose super.allQuery 
                    with a filter that returns rows where isActive is true */
}

trait HasName[Tuple <: Product] extends Table[Tuple] {
  def name = column[String]("name")

  def * = super.* ~ name
}

trait SortedByName[Tuple <: Product] extends HasName[Tuple {
  override def allQuery = super.allQuery /* compose somehow 
                                             with (_ <- Query orderBy name */
}

Can I do these kinds of things with ScalaQuery? The main sticking points are:

  1. How do I cleanly compose the filters in SoftDeletable.allQuery and the sort in SortedByName.allQuery with BaseModel.allQuery?

  2. By adding columns in subclass implementations of the * method, the tuple type parameter to Table no latter matches - is there a way for these traits to incrementally add new types to the columns tuple in the ultimate concrete class? (I don't expect there to be, but it would be nice if there was something I'm missing).

  3. I need to repeat the long tuple declaration in every trait, which becomes very unwieldy if a table has five or six columns. Is there something I can do with type members to avoid having to do things like:

    case class Foo

class Foos[(Int,Int,Boolean,String), Foo] extends 
  Table[(Int,Int,Boolean,String)] with 
  SoftDeletable[(Int,Int,Boolean,String), Foo] with 
  SortedByName[(Int,Int,Boolean,String), Foo] with 
  HasName[(Int,Int,Boolean,String)] {
}

Can I avoid all this repetition? Based on a suggestion from jesnor on IRC, I was able to avoid some of this like so:

abstract class SoftDeletableBaseModel[TupleClass <: Product, CaseClass](tableName: String)
        extends BaseModel[TupleClass, CaseClass](tableName)
        with SoftDeletable[TupleClass,CaseClass]

In other words, by combining specific traits together, I don't need to repeat the entire tuple declaration; of course, the disadvantage is that easy mixing-in of various traits is no longer possible - I need to create lots of specific subclasses to avoid this repetition. Is there another way?

Update: So I realized that I don't need to use separate CaseClass and TupleClass type parameters. Since case classes implement Product*, you can just pass the case class name into Table, which solves the problem in 3:

trait SoftDeletable[CaseClass] extends BaseModel[CaseClass] { ... }

class Models extends BaseModel[Model]("models") with SoftDeletable[Model] { ... }

Upvotes: 13

Views: 472

Answers (1)

nafg
nafg

Reputation: 2534

If your issue is only adding the sort, isn't it just a matter of flatMap?

def sortBy[T,U,C](q: Query[T,U], col: NamedColumn[C]) = q.flatMap(_ => Query orderBy col)

Upvotes: 1

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