Groot

With Groot you can convert JSON dictionaries and arrays to and from Core Data managed objects.

Requirements

Groot supports OS X 10.8+ and iOS 6.0+.

Installation

Add the following to your Podfile and run $ pod install.

pod 'Groot'

If you don't have CocoaPods installed or integrated into your project, you can learn how to do so here.

Usage

Suppose we would like to convert the JSON returned by a Comic Database web service into our own model objects. The JSON could look something like this:

[
    {
        "id": "1699",
        "name": "Batman",
        "powers": [
            {
                "id": "4",
                "name": "Agility"
            },
            {
                "id": "9",
                "name": "Insanely Rich"
            }
        ],
        "publisher": {
            "id": "10",
            "name": "DC Comics"
        },
        "real_name": "Bruce Wayne"
    },
	...
]

We could model this in Core Data using 3 entities: Character, Power and Publisher.

Note that we don't need to name our attributes as in the JSON. The serialization process can be customized by adding certain information to the user dictionary provided in Core Data entities, attributes and relationships.

For instance, we can specify that the identifier attribute will be mapped from the id JSON key path, and that its value will be transformed using an NSValueTransformer named GRTTestTransfomer.

Now we can easily convert JSON data and insert the corresponding managed objects with a simple method call:

NSDictionary *batmanJSON = @{
	@"id": @"1699",
	@"name": @"Batman",
	@"real_name": @"Bruce Wayne",
	@"powers": @[
	@{
		@"id": @"4",
		@"name": @"Agility"
	},
	@{
		@"id": @"9",
		@"name": @"Insanely Rich"
	}],
	@"publisher": @{
		@"id": @"10",
		@"name": @"DC Comics"
	}
};

NSError *error = nil;
NSManagedObject *batman = [GRTJSONSerialization insertObjectForEntityName:@"Character"
													   fromJSONDictionary:batmanJSON
												   inManagedObjectContext:context
														            error:&error];

Merging data

When inserting data, Groot does not check if the serialized managed objects already exist and simply treats them as new.

If instead, you would like to merge (that is, create or update) the serialized managed objects, then you need to tell Groot how to uniquely identify your model objects. You can do that by associating the identityAttribute key with the name of an attribute in the entity user info dictionary.

In our sample, all of our models are identified by the identifier attribute.

Now we can update the Batman character we just inserted in the previous snippet:

NSDictionary *updateJSON = @{
	@"id": @"1699",
	@"real_name": @"Guille Gonzalez"
}

// This will return the previously created managed object
NSManagedObject *batman = [GRTJSONSerialization mergeObjectForEntityName:@"Character"
													  fromJSONDictionary:batmanJSON
												  inManagedObjectContext:context
														           error:NULL];

If you want to merge a JSON array, its better to call mergeObjectsForEntityName:fromJSONArray:inManagedObjectContext:error:. This method will perform a single fetch per entity regardless of the number of objects in the JSON array.

Back to JSON

You can convert managed objects into their JSON representations by using JSONDictionaryFromManagedObject: or JSONArrayFromManagedObjects:.

NSDictionary *JSONDictionary = [GRTJSONSerialization JSONDictionaryFromManagedObject:someManagedObject];

Contact

Guillermo Gonzalez
@gonzalezreal

License

Groot is available under the MIT license. See LICENSE.