Slick 3.1.1模糊隐含值涉及过滤器和隐式CanBeQueryCondition

Question

I have been trying to create a Generic Dao over Slick 3.1.1 and it includes a generic filter that competes with JPA's findByExample , see the following files:

• GenericDaoImpl.scala Generic level reusable across all Models
• UserDao.scala Generic plus customizations for the User model
• UserService.scala Wraps the UserDao into more services level functionality

In this last file I try to use the generic filter function to find a user by its registered email, like this:

// this will implicitly exec and wait indefinitely for the 
// db.run Future to complete
import dao.ExecHelper._ 

def findByEmail(email: String): Option[UserRow] = {
  userDao.filter(_.email === email).headOption
}

but this produces the compiler error:

[error] /home/bravegag/code/play-authenticate-usage-scala/app/services/UserService.scala:35: value === is not a member of String
[error]     userDao.filter(email === _.email).headOption
[error]                          ^
[error] /home/bravegag/code/play-authenticate-usage-scala/app/services/UserService.scala:35: ambiguous implicit values:
[error]  both value BooleanOptionColumnCanBeQueryCondition in object CanBeQueryCondition of type => slick.lifted.CanBeQueryCondition[slick.lifted.Rep[Option[Boolean]]]
[error]  and value BooleanCanBeQueryCondition in object CanBeQueryCondition of type => slick.lifted.CanBeQueryCondition[Boolean]
[error]  match expected type slick.lifted.CanBeQueryCondition[Nothing]
[error]     userDao.filter(email === _.email).headOption
[error]                   ^

Can anyone advice on how the implicit declaration of the filter function below can be improved to solve this compiler error?

The implementation of the filter function (found in GenericDaoImpl.scala ) is:

// T is defined above as T <: Table[E] with IdentifyableTable[PK]

override def filter[C <: Rep[_]](expr: T => C)
  (implicit wt: CanBeQueryCondition[C]) : Future[Seq[E]] = 
    db.run(tableQuery.filter(expr).result)

Answer 1

As far as I can see you are simply lacking you profile API import in UserService .

Just add there this import: import profile.api._ and it should work.

EDIT: BTW I see many people building their own version of base CRUDs for Slick. Did you try some existing thin libraries doing just that eg here: https://github.com/VirtusLab/unicorn ? It's not really related to this question but it may be worth to take a look.