Dynamic query with optional where clauses using Slick 3

A simpler approach without for comprehension:

import slick.lifted.LiteralColumn

val depLocOpt = Option[Long]
val slickFlights = TableQuery[Flights]
val query = slickFlights.filter { sf => 
  if (depLocOpt.isDefined) sf.departureLocation === depLocOpt.get
  else                     LiteralColumn(true)
}

UPDATE: you can shorten it more with fold:

val depLocOpt = Option[Long]
val slickFlights = TableQuery[Flights]
val query = slickFlights.filter { sf => 
  depLocOpt.fold(true.bind)(sf.departureLocation === _)
}

January 2019

No more need to invent your own wheels!

At last Slick 3.3.0 includes the following helpers:

• filterOpt
• filterIf

So, for example:

case class User(id: Long, name: String, age: Int)
case class UserFilter(name: Option[String], age: Option[Int])

val users = TableQuery[UsersTable]

def findUsers(filter: UserFilter): Future[Seq[User]] = db run {
  users
    .filterOpt(filter.name){ case (table, name) =>
      table.name === name
    }
    .filterOpt(filter.age){ case (table, age) =>
      table.age === age
    }
    .result
}

For the benefit of anyone else trying to get optional filters working in Slick, have a look at the answer here: right usage of slick filter. I finally managed to get it working with the following:

def search(departureLocation: Option[String], arrivalLocation: Option[String]) = {
  val query = for {
    flight <- slickFlights.filter(f =>
       departureLocation.map(d => 
         f.departureLocation === d).getOrElse(slick.lifted.LiteralColumn(true)) && 
       arrivalLocation.map(a => 
         f.arrivalLocation === a).getOrElse(slick.lifted.LiteralColumn(true))
    )
  } yield flight

The key bit being the .getOrElse(slick.lifted.LiteralColumn(true)) on the end of the map, which causes Slick to render SQL as follows if for example only the departureLocation is set...

select * from `flight` 
where (`departureLocation` = 'JFK') and true

whereas without it the SQL looked like...

select * from `flight` 
where (`departureLocation` = 'JFK') and (`arrivalLocation` = '')

which obviously meant that it came back with no rows.