Merging with deletion about groot HOT 8 CLOSED

This is something that could be implemented inside Groot, or you can do it in a category.

Here's what I would do:

- (void)updateAndDelete {
    NSArray *objects = [GRTJSONSerialization mergeObjectsForEntityName:@"Test"
                                                         fromJSONArray:JSONResponse
                                                inManagedObjectContext:myContext
                                                                 error:&error];

    // Fetch unmodified objects
    NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Test"];
    fetchRequest.predicate = [NSPredicate predicateWithFormat:@"NOT (self IN %@)", objects];
    fetchRequest.includesPropertyValues = NO; // We just need the object IDs

    NSArray *objectsToDelete = [myContext executeFetchRequest:fetchRequest error:NULL];

    // Delete unmodified objects
    for (NSManagedObject *obj in objectsToDelete) {
        [myContext deleteObject:obj];
    }

    // Save...
}

from groot.

Nice, clear and concise. Thanks a lot! ;-)

from groot.

No problem. I will think about adding this functionality, but in the meantime you can just use that code.

from groot.

Reopening so that it's visible to everyone.

from groot.

I just realized that the code you provided only works on the top level entity. For instance, take the following JSON structure (mapped to Category and Item Core Data entities):

[
  {
    id: 1,
    title: "Category",
    items: [
      {
        id: 1,
        title: "Item #1"
      },
      {
        id: 2,
        title: "Item #2"
      }
    ]
  }
]

Now, when fetching all Category entities which have a too-many relationship with Item entities via items, and one of the items is removed from the JSON, it is not deleted from my Core Data store. The updateAndDelete method you suggested only works on top-level entities (Category in this example).

Any ideas on how to tackle this problem are greatly appreciated!

from groot.

You can setup a delete rule in your relationship to cascade deletes. Check the Core Data Inspector with your items relationship selected.

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Sorry, I misread your question. The delete rule has no use here. In that case, the only viable solution would be to have a deleted field in your JSON that is mapped to your model. After processing the JSON you could perform a fetch request for all deleted items and remove them from the database.

from groot.

Thanks i use the folllowing swift version now:

func remainingObjectsFromJSONArray<T: NSManagedObject>(array: JSONArray, inContext context: NSManagedObjectContext) throws -> [T] {
    let objects: [T] = try objectsFromJSONArray(array, inContext:context)

    let entity = T.entityInManagedObjectContext(context)

    let fetchRequest = NSFetchRequest(entityName: entity.name!);
    fetchRequest.predicate = NSPredicate(format: "NOT (self IN %@)", objects);
    fetchRequest.includesPropertyValues = false; // We just need the object IDs

    let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
    try context.executeRequest(deleteRequest)

    return objects
}

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