Deleting with one-to-many relationship

Question

I have a one-to-many relationship:

class GameSystem: Object {
dynamic var gameSystemName = ""
}

class games: Object {
dynamic var gameSystemName = gameSystemName().name
dynamic var gameTitle = ""
dynamic var gameGenre = ""
}

The gameSystemNames are currently displayed on a TableView. If the user deletes a gameSystemName, I want that gameSystemName along with all of that system's games deleted.

The code I'm currently using will only delete the GameSystem, but leaves all the games.

    func deleteRowAtIndexPath(indexPath: NSIndexPath) {
    let realm = Realm()
    let objectToDelete = gameSystems[indexPath.row]
    realm.write {
        realm.delete(objectToDelete)
    }
    gameSystemTableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
    gameSystems = Realm(path: Realm.defaultPath).objects(GameSystem)
}

I'm assuming there's a simple way to do this.

score 7 · Accepted Answer · answered Sep 05 '15 at 10:15

If you keep your model as it is, the solution would be to query first for the relevant objects of the relation Game:

// …
let objectToDelete = gameSystems[indexPath.row]
let gameSystemName = objectToDelete.gameSystemName
realm.write {
    let games = realm.objects(Game).filter("gameSystemName = ?", gameSystemName)
    realm.delete(games)
    realm.delete(objectToDelete)
}
// …

Model Recommendation

I'd propose instead that you add an explicit link to your model, instead of expressing the relationship through a loosely linked foreign key. But the object-mapping is very individual and may be dependent on further constraints going beyond the scope of your question and this answer. For further reference, that would look like below:

 class GameSystem : Object {
      dynamic var name = ""
      let games = List<Game>()
 }

 class Game : Object {
      dynamic var title = ""
      dynamic var genre = ""

      // Use a backlink
      // (https://realm.io/docs/swift/latest/#inverse-relationships)
      dynamic var gameSystem: GameSystem? {
           return linkingObjects(GameSystem.self, forProperty: "games").first
      }
 }

If you setup your model like this, you can delete your games very easy:

// …
let objectToDelete = gameSystems[indexPath.row]
realm.write {
    realm.delete(objectToDelete.games)
    realm.delete(objectToDelete)
}
// …

Note: In the future, Realm will bring Cascading Deletes as feature. Once that is released, you won't even need to take care of the manual deletion of associated games, but you will rather be able to declare the strong relationship in your model, so that the Games are automatically deleted.

Alternative Link Declaration

You can also declare your link vice-versa, but that would make it likely harder to use a feature like Cascading Deletes in the future. However the code to delete them for now would look the same as above.

 class GameSystem : Object {
      dynamic var name = ""

      // Use a backlink
      // (https://realm.io/docs/swift/latest/#inverse-relationships)
      dynamic var games: [Game] {
           return linkingObjects(Game.self, forProperty: "gameSystem")
      }
 }

 class Game : Object {
      dynamic var title = ""
      dynamic var genre = ""
      let gameSystem: GameSystem? = nil
 }

marius, i appreciate your thoughtful answer. thanks for helping! — ultraflex, Sep 06 '15 at 05:38

score 0 · Answer 2 · edited Mar 15 '19 at 13:14

It is very easy to delete the Parent as well as childrens in REALM SWIFT... You just need to write a small piece of code.

Here I am trying to delete my main category called "Swift" and whenever my main category gets deleted all the Sub Categories are also deleted...

do{
      try realm.write({
          realm.delete(Category.items)
          realm.delete(Category)
      })
}catch{
       print("ERROR WHILE DELETING CELL ::: \(error)")
}

In short to delete subcategories all you need is to place "items" after . followed by parent name.

Deleting with one-to-many relationship

2 Answers2

Model Recommendation

Alternative Link Declaration

Linked