How do you run a patch/partial database UPDATE in Scala Slick?

Question

We\'d like to run a patch/partial UPDATE with Slick (3.0.0) so that we only modify some of the fields in a record. Exactly which fields will be updated exactly will

Answer 1

You already have answers as written by @pedrorijo91 and @thirstycow but i'll try to explain why this doesnt work.

I'm havent used slick 3 but im guessing its because the map function doesnt return a consistent type for it to run update against. As a thought experiment, if you cut your call at map what do you think the type will be?

val partialQuery:??? = people.filter(_.name === "M Odersky")
       .map(p => 
           (name, age) match {
              case (Some(_), Some(_)) => (p.name, p.age)
              case (Some(_), None)    => (p.name)
              case (None   , Some(_)) => (p.age)
           }
       );

val fullQuery:??? = partialQuery.update {
       (name, age) match {
          case (Some(_), Some(_)) => (name.get, age.get)
          case (Some(_), None)    => (name.get)
          case (None   , Some(_)) => (age.get)
       }    
}

The matcher returns different "shapes" at compile time which im guessing will revert to Any type.

Answer 2

My best guess would be to run a plain SQL query

Even if the SQL query has 2 parts, the relational database management system (postgresql, mysql, etc) is able to tune the query under the hoods.

I'm not sure if in this case Slick is able to optimize, but in several cases it also optimizes the queries by itself.

Typical update:

def updateRecord(id: Long, field1: Int) = {
    db.withSession {
      self.filter(_.id === id).map(_.field1).update(field1)
    }
}

Doing your type of update would require a bit more logic like you did. Don't think it's possible to simplify if you only know at runtime which fields to change. But you can force the update, using existing value for the field on the record as a fallback (may lead to more updates on DB than it should)

def updateRecord(id: Long, field1: Option[Int], field2: Option[Int]) = {
    db.withSession {
        self.filter(_.id === id).map(_.field1, _.field2).update(field1.getOrElse(existingValue1), field2.getOrElse(existingValue2)) 
    }
}

Answer 3

Why not do the pattern matching before constructing the update query?

def patchPerson(name: Option[String], age: Option[Int]) = {
   val query = people.filter(_.name === "M Odersky")
   (name, age) match {
     case (Some(name), Some(age)) =>
       query.map(p => (p.name, p.age)).update(name, age)
     case (Some(name), None) =>
       query.map(p => p.name).update(name)
     case (None, Some(age)) =>
       query.map(p => p.age).update(age)
   }
}