未指定的值参数rconv

Question

I had these lines in my code

val x = database.withSession { implicit session => 
  StaticQuery.queryNA[Long](s"select id from .....")
}

val y = database.withSession { implicit session => 
  StaticQuery.queryNA[Long](s"select id1 from .....")
}

val z = database.withSession { implicit session => 
  StaticQuery.queryNA[(Long, Long)](s"select id1, id2 from .....")
}

In order to minimize code duplication I changed my code to

def genericExec[T](query: String) : List[T] = {
  database.withSession { implicit session => 
    StaticQuery.queryNA[T](query).list
  }
}

for {
  x <- genericExec[Long](query1)
  y <- genericExec[Long](query2)
  z <- genericExec[(Long, Long)](query3)
} {...}

Of course I get an error now that

Error:(16, 32) not enough arguments for method queryNA: (implicit rconv: scala.slick.jdbc.GetResult[T])scala.slick.jdbc.StaticQuery[Unit,T].
Unspecified value parameter rconv.
         StaticQuery.queryNA[T](query).list

Since the type T is totally generic its impossible for me to provide all types of conversions. So how can I keep my generic implementation and just provide the conversions which my type T is actually using in my code (aka Long, and (Long, Long)

Answer 1

Because queryNA has a GetResult constraint on T , your function has to have the same constraint. You need to tell your generic method that it is only valid for types T that have a GetResult defined, so:

def genericExec[T : GetResult](query: String) : List[T] = ...

or equivalently:

def genericExec[T](query: String)(implicit rconv: GetResult[T]) : List[T] = ...