Slick 3.1.1 ambiguous implicit values involving filter and implicit CanBeQueryCondition

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)

Solution

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 e.g. here: https://github.com/VirtusLab/unicorn ? It's not really related to this question but it may be worth to take a look.