How to save POJO with the Relation annotation in Room Peristence Library?

Question

I am currently playing with Room in order to compare it with Realm and I already have so many question about the best way to do things.

In my sample app, I have a really simple model in which one a Person can have Cats and Dogs.

Here the java classes.

Cat and Dog classes inherit from an Animal class :

public abstract class RoomAnimal
{

  @PrimaryKey
  public int id;

  public int age;

  public String name;

}

The Cat class :

@Entity(tableName = "cat")
public final class RoomCat
    extends RoomAnimal
{

}

The Dog class :

@Entity(tableName = "dog")
public final class RoomDog
    extends RoomAnimal
{

  public enum RoomColor
  {
    Black, White
  }

  public static final class RoomColorConverter
  {

    @TypeConverter
    public RoomColor fromString(String color)
    {
      return color != null ? RoomColor.valueOf(color) : null;
    }

    @TypeConverter
    public String fromRealmColor(RoomColor color)
    {
      return color.toString();
    }

  }

  @TypeConverters(RoomColorConverter.class)
  public RoomColor color;

}

The Person class :

@Entity(tableName = "person")
public final class RoomPerson
{

  @PrimaryKey
  public int id;

  public String name;

}

I also have a POJO in order to modelize the fact that a user can have cats and dogs :

public final class RoomPersonWithAnimals
{

  @Embedded
  public RoomPerson person;

  @Relation(parentColumn = "id", entityColumn = "id", entity = RoomDog.class)
  public List<RoomDog> dogs;

  @Relation(parentColumn = "id", entityColumn = "id", entity = RoomCat.class)
  public List<RoomCat> cats;

}

The question is : how to save a list of RoomPersonWithAnimals objects ?

I cannot use the Insert annotation in a Dao class because the RoomPersonWithAnimals is not an Entity.

For each objects of my list of RoomPersonWithAnimals should I run 3 requests ?

• one in order to insert the person attribute ;
• one in order to insert the list of cats ;
• one in order to insert the list of dogs ;

Thank you in advance for your help !

Answer 1

how to save a list of RoomPersonWithAnimals objects ?

You don't, at least in the 1.0.0-alpha6 version of Room, as those are not entities.

For each objects of my list of RoomPersonWithAnimals should I play 3 requests ?

Yes. You can use runInTransaction() to perform those three operations inside a single SQLite transaction.