Android Room apply constraint to Relation

Question

I'm aware Room lets us establish 1-N relations with the @Relation keyword. Although I'd like to know if it's possible to apply conditions to this relationship.

Let's say that I have the following POJO

class UserAndPets {
    @Embedded
    lateinit var user: User

    @Relation(entityColumn = "ownerId", parentColumn = "userId")
    lateinit var pets: List<Pets>
}

interface UserDao {
    @Query("SELECT * FROM users WHERE userId = :userId LIMIT 1")
    fun getUserAndPetsForUserId(userId: String): UserAndPets?
}

The above method lets me query a User and all his pets. Although is there a way for me to query the User and his last 10 pets for example? Or a User and all his Pets that would be a certain type?

Thanks

Answer 1

If the Id field in Pets is auto-incremented then this query should give you the result you are looking for:

@Query("SELECT * FROM pets WHERE ownerId = :userId ORDER BY Id DESC LIMIT 10")

By the way, the "LIMIT 1" in your Users query is unneccessary, the query would always return a single user.