scala - Slick 3 reusable generic repository

Question

I am experiencing issues making Slick's TableQuery used in a generic fashion.

Observe the regular situation:

class AccountRepository {
override protected val dbConfig = DatabaseConfigProvider.get[JdbcProfile](Play.current)
val accounts = TableQuery[Accounts]
def all = db.run(accounts.result)
...

The idea would be to extract everything possible into generic trait or abstract class in order to avoid repetition. For the sake of simplicity I included only the problematic code.

abstract class GenericRepository[T] extends HasDatabaseConfig[JdbcProfile] {
override protected val dbConfig = DatabaseConfigProvider.get[JdbcProfile(Play.current)
val table = TableQuery[T]
}

And to use it like:

class AccountRepository extends GenericRepository[Accounts] {

However, that creates a compilation error:

type arguments [T] conform to the bounds of none of the overloaded alternatives of value apply: [E <: slick.lifted.AbstractTable[]]=> slick.lifted.TableQuery[E] [E <: slick.lifted.AbstractTable[]](cons: slick.lifted.Tag => E)slick.lifted.TableQuery[E]

Trying to fix the issue by setting a boundary doesn't help as well.

abstract class GenericRepository[T <: slick.lifted.AbstractTable[T]] extends HasDatabaseConfig[JdbcProfile] {

However, we end up with a different error:

class type required but T found

at following place:

val table = TableQuery[T]

Any idea about the solution?

Answer 1

You have to pass table query manually,

 abstract class GenericRepository[T <: slick.lifted.AbstractTable[_]](query: TableQuery[T])

and in implementation,

class AccountRepository extends GenericRepository[Accounts](TableQuery[Accounts])

I hope this will solve your problem.