We can describe how you interact with RestKit by looking at the following sample sequence diagram for getting data:

RestKit usage sequence diagram

When you, as a Caller, wish to get data from a Remote web service, you ask for it on RestKit. It then decides on a strategy and gets the paths and mapping information by checking a configuration for the particular type of objects that you want. RestKit uses AFNetworking under the hood to do the actual data retrieving from the Remote and parsing in to NSDictionary or NSArray. AFNetworking itself checks with NSURLCache if it should make a request again, or use the cache. (We'll discuss this in detail in Chapter 4, Advanced Stuff in the HTTP Caching section). AFNetworking then gives back the response to a RestKit, along with all additional information, which were gathered during the "request-response-parse sequence".

If you're not using Core Data for this type of objects (we can call it "In-Memory object"), RestKit creates new instances of the object, and maps a response data to it. It then returns the object(s) back to the Caller.

Now if you are using Core Data, and the object is a Managed object, RestKit will first check with the Core Data if it already has an object with a similar ID. It will also check if the object in response has a deleted flag. It will then do the mapping and update/delete the particular object, and check how to deal with orphan objects. At the end, it will return the resultant objects to the user. Core Data itself will notify all its observers via Key Value Observing (KVO) about the changes.