光滑：比较Rep [Option [Blob]]与Rep [Int]

Question

I am using Slick to analyze a legacy MySQL database (with MyISAM engine). And I'm using implicit classes to navigate through entities, eg user.logs with this code:

implicit class UserNav(user: User) {
    def logs = Logs.filter(_.userId === user.id)
}

However, in this case the key is an INT but the foreign key is a BLOB. Using a MySQL client I can run select userId * 1 from logs to get an INT from the BLOB, and I can even join despite the different datatypes. But with Slick I get a compile errors for the code above.

error: Cannot perform option-mapped operation [ERROR]
with type: (Option[java.sql.Blob], Int) => R [ERROR]   
for base type:(java.sql.Blob, java.sql.Blob) => Boolean

error: ambiguous implicit values:
both value BooleanOptionColumnCanBeQueryCondition in object CanBeQueryCondition of type => slick.lifted.CanBeQueryCondition[slick.lifted.Rep[Option[Boolean]]]
and value BooleanCanBeQueryCondition in object CanBeQueryCondition of type => slick.lifted.CanBeQueryCondition[Boolean]
match expected type slick.lifted.CanBeQueryCondition[Nothing]

Any idea how to solve this?

Answer 1

As I found out by trying, just pretending the column has a different data type works.

So besides the original val in class Log (which extends Table[LogRow] )

val userId: Rep[Option[java.sql.Blob]] = column[Option[java.sql.Blob]]("userId", O.Default(None))

I added

val userId_asInt: Rep[Option[Int]] = column[Option[Int]]("userId", O.Default(None))

and changed the navigation def to

def logs = Logs.filter(_.userId_asInt === user.id)

This did the trick – at least with MySQL/MyISAM (no idea if this works with other engines or even other DBMS).

Instead I could also have replaced the data type in original val userId , but then I would also have to change that data type all over the place like in Log.* and Log.? ...