Cascade delete complex objects: Nested objects with and without @PrimaryKey

[alexei-28]

Realm ver. 4.1.0

In my Android application I use Realm. In Realm I has Merchant objects. I need to delete ALL of them.
The Merchant is a complex object that contain nested objects with and WITHOUT @PrimaryKey.

Here code:

public class Merchant extends RealmObject {
    @PrimaryKey
    private long id;
    private LocalizedString name;
    private Category category;
    private Image preview;
    private RealmList<Product> products = new RealmList<>();
    private boolean favorite;


  public void cascadeDelete() {
        name.cascadeDelete();
        if (category != null) {
            category.cascadeDelete();
        }
        if (preview != null) {
            preview.cascadeDelete();
        }
        for (int index = products.size() - 1; index >= 0; index--) {
            Product product = products.get(index);
            product.cascadeDelete();
        }
           deleteFromRealm(); // delete this object
	}
}

Here nested objects:

public class LocalizedString extends RealmObject {
    private RealmList<TranslatedString> translations = new RealmList<>();

    public void cascadeDelete() {
        for (int index = translations.size() - 1; index >= 0; index--) {
            TranslatedString currentTranslatedString = translations.get(index);
            currentTranslatedString.deleteFromRealm();
        }
            deleteFromRealm(); // delete this object
	}
}
	

 public class TranslatedString extends RealmObject {
    private String locale;
    private String value;
  }



public class Category extends RealmObject {
    @PrimaryKey
    private long id;
    private LocalizedString name;
    private Image image;
    private Date createdAt = new Date();

    public void cascadeDelete() {
        name.cascadeDelete();
        if (image != null) {
            image.cascadeDelete();
        }
          deleteFromRealm(); // delete this object
      }
}
	

public class Image extends RealmObject {
    @PrimaryKey
    private long id;
    private ImageFormats formats;
    private Date updatedAt = new Date();

    public void cascadeDelete() {
        formats.cascadeDelete();
        deleteFromRealm(); // delete this object
    }
}


public class ImageFormats extends RealmObject {
    private ImageSource reference;
    private ImageSource average;

    public void cascadeDelete() {
        if (reference != null) {
            reference.deleteFromRealm();
        }
        if (average!= null) {
            average.deleteFromRealm();
        }
        deleteFromRealm(); // delete this object
	}
}


public class ImageSource extends RealmObject {
    private int width;
    private int height;
}


public class Product extends RealmObject {
    @PrimaryKey
    private long id;
    private LocalizedString name;
    private Image preview;
    private float price;

    public void cascadeDelete() {
        name.cascadeDelete();
        if (preview!= null) {
            preview.cascadeDelete();
        }
          deleteFromRealm(); // delete this object
   }
}

And here code that call delete of ALL merchants:

public static void updateMerchants(final List<Merchant> incomingMerchantsList) {
       Realm realm = Realm.getDefaultInstance();
       try {
           realm.executeTransaction(new Realm.Transaction() {
               @Override
               public void execute(Realm realm) {
                   RealmResults<Merchant> localMerchantList = getMerchants(realm, new Bundle(), null);
                    for (Merchant localMerchant : localMerchantList) {
                        localMerchant.cascadeDelete();
                   }
                   localMerchantList.deleteAllFromRealm();
               }
           });
       } finally {
           realm.close();
       }
}

As you can see I delete nested objects by use custom method cascadeDelete()

Questions:

1. Is it correct approach? Is I MUST call cascadeDelete() to delete nested objects?
2. I think it too much code. Has any solution with less code?

Thanks.

[cmelchior]

Yes, the above code is currently what is required to make cascading deletes work. You are correct it is quite a lot of boilerplate, so it is something we want to add natively to Realm. You can follow #5678 for progress on it.

[realm-probot]

Hey - looks like you forgot to add a T:* label - could you please add one?

[alexei-28]

Yes, the above code is currently what is required to make cascading deletes work. You are correct it is quite a lot of boilerplate, so it is something we want to add natively to Realm. You can follow #5678 for progress on it.

it would be very good

[alexei-28]

Here my incoming json for merchant

{
  "id": 1,
  "name": "name of merchant",
  "category": {
    "id": 2,
    "name": "name of category",
    "image": {
      "id": 2,
      "formats": {
        "reference": {
          "url": "m1_cat2_im2_ref"
        }
      }
    }
  },
  "offers": [
    {
      "id": 1,
      "name": "name of offer",
      "category": {
        "id": 2,
        "name": "name of category",
        "image": {
          "id": 2,
          "formats": {
            "reference": {
              "url": "m1_cat2_im2_ref"
            }
          }
        }
      }
    },
    {
      "id": 2,
      "name": "name of offer2",
      "category": {
        "id": 2,
        "name": "name of category",
        "image": {
          "id": 2,
          "formats": {
            "reference": {
              "url": "m1_cat2_im2_ref"
            }
          }
        }
      }
    }
  ]
}

As you can see merchant and offers has same nested category.

Here my pojos:

public class Merchant extends RealmObject {
    @PrimaryKey
    private long id;
    private String name;
   private Category category;

    public void cascadeDelete() {
         category.cascadeDeleteWithoutPK();
         for (int index = offers.size() - 1; index >= 0; index--) {
             Offer currentOffer = offers.get(index);
             currentOffer.cascadeDeleteWithoutPK();
         }
         deleteFromRealm(); // delete this object
    }
}

public class Offer extends RealmObject {
    @PrimaryKey
    private long id;
    private String name;
    private Category category;

 public void cascadeDeleteWithoutPK() {
       Debug.d(TAG, "cascadeDeleteWithoutPK_before_delete_offer:");
       category.cascadeDeleteWithoutPK();
      deleteFromRealm(); // delete this object
      }
}

public class Category extends RealmObject {
    @PrimaryKey
    private long id;
    private String name;
    private Image image;

  public void cascadeDeleteWithoutPK() {
      Debug.d(TAG, "cascadeDeleteWithoutPK_before_delete_image:");
      image.cascadeDeleteWithoutPK();
      deleteFromRealm(); // delete this object
      Debug.d(TAG, "cascadeDeleteWithoutPK_after_delete_image:");
  }
}

public class Image extends RealmObject {
    @PrimaryKey
    private long id;
    private ImageFormats formats;

   public void cascadeDeleteWithoutPK() {
      formats.cascadeDeleteWithoutPK();
  }
}

POJO ImageFormats has no @PrimaryKey annotation

public class ImageFormats extends RealmObject {
    private ImageSource reference;

 public void cascadeDeleteWithoutPK() {
     reference.deleteFromRealm();
 }
}

Here code the try to delete all merchant objects in realm:

public static void updateMerchantList(final List<Merchant> incomingMerchantsList) {
       Realm realm = Realm.getDefaultInstance();
       try {
           realm.executeTransaction(new Realm.Transaction() {
               @Override
               public void execute(Realm realm) {
                   RealmResults<Merchant> localMerchantList = getMerchants(realm, new Bundle(), null);
                   for (Merchant localMerchant : localMerchantList) {
                       localMerchant.cascadeDelete();
                   } 
                    // insert new merchant to Realm
                   RealmList<Merchant> incomingMerchantsRealmList = new RealmList<>();
                   incomingMerchantsRealmList.addAll(incomingMerchantsList);
                   List<Merchant> updateMerchantList = 
                          realm.copyToRealmOrUpdate(incomingMerchantsRealmList);
                 }
           });
       } finally {
           realm.close();     
       }
   }

After this code in realm has 1 merchant , 2 offers, 3 categories, 3 images and 3 ImageFormats objects. Nice. It's correct.

But as result it not delete all ImageFormats.
It's delete only first ImageFormats. Rest TWO objects ImageFormats is stay in Realm forever.

Here logs:

myproject.model.Category(26347): cascadeDeleteWithoutPK_before_delete_image:
myproject.model.Category(26347): testImage: category.id = 2
myproject.model.Category(26347): 	image = 
myproject.model.Category(26347): 	Im{id = 2
myproject.model.Category(26347): 	formats = 
myproject.model.Category(26347): 	{		reference= 
myproject.model.Category(26347):         IS{url = 'm1_cat2_im2_ref'}}}


myproject.model.Offer(26347): cascadeDeleteWithoutPK_before_delete_offer:
myproject.model.Offer(26347): 	testOffer: offer_id = 2
myproject.model.Offer(26347): 	category = 2
myproject.model.Offer(26347): 	image = 
myproject.model.Offer(26347): 	Im{id = 2
myproject.model.Offer(26347): 	formats = 
myproject.model.Offer(26347): 	{		reference= null}}

as you can see here reference now is NULL. And when I call cascadeDeleteWithoutPK_before_delete_image again:

myproject.model.Category(26347): cascadeDeleteWithoutPK_before_delete_image:
myproject.model.Category(26347): testImage: category.id = 2
myproject.model.Category(26347): 	image = 
myproject.model.Category(26347): 	Im{id = 2
myproject.model.Category(26347): 	formats = 
myproject.model.Category(26347): 	{		reference= null}}

so... nothing delete. Because category in merchant and in offer has same ID = 2. As result I can't delete rest of ImageFormats objects from Realm. I delete only FIRST ImageFormats from Realm. But rest TWO ImageFormats is stay in Realm.
How I can delete ALL (in this example three) OF THE ImageFormats objects?