Multiple left joins using slick?

Question

I have the following slick entities:

class Person(personId, houseId, carId)
class House(houseId)
class Car(carId)

I want to select a Person and their optional house and car, my query is:

val query = personTable
      .filter(_.personId === personId)
      .joinLeft(houseTable)
      .on(_.houseId === _.houseId)
      .joinLeft(carTable)
      .on(_._1.carId === _.carId)
      .result
      .headOption

However, the return type of the query looks a little funny, I'd expect it to be a tuple(person, house, car):

Option[(Person, Option[House], Option[Car])]

But it's actually a tuple(tuple(person, house), car):

Option[((Person, Option[House]), Option[Car])]

The data that comes back does seem correct, its just in an unusual structure, maybe I'm not performing the multiple joins correctly above?

Perhaps if you try to rewrite this within a for-comprehension (look at the example in the [applicative join](http://slick.lightbend.com/doc/3.0.0/queries.html?highlight=join#applicative-joins)), you would be able to change the format of the query to return a single tuple. Since for-comprehensions are just, nice, syntactic sugars, a `map` would probably do the job as well — Yaneeve, Oct 11 '18 at 11:35

score 5 · Accepted Answer · answered Oct 11 '18 at 15:01

Things look normal to me.

If you don't like the current datatype, you can map in your query to change it, like this e.g:

val query = personTable
      .filter(_.personId === personId)
      .joinLeft(houseTable)
      .on(_.houseId === _.houseId)
      .joinLeft(carTable)
      .on(_._1.carId === _.carId)
      .map{case((person, houseOpt), carOpt) => (person, houseOpt, carOpt)}
      .result
      .headOption

Multiple left joins using slick?

1 Answers1