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ioscocoacore-datanskeyedarchiver

NSKeyedArchiver vs Core Data

I am building an app with Objective-C and I would like to persist data. I am hesitating between NSKeyedArchiver and core Data. I am aware there are plenty of ressources about this on the web (including Objective-C best choice for saving data) but I am still doubtful about the one I should use. Here are the two things that make me wonder :

(1) I am assuming I will have around 1000-10000 objects to handle for a data volume of 1-10 Mb. I will do standard database queries on these objects. I would like to be able to load all these objects on launching and to save them from time to time -- a 1 second processing time for loading or saving would be fine by me.

(2) For the moment my model is rather intricate : for instance classA contains among other properties an array of classB which is itself formed by (among other) a property of type classC and a property of type classD. And class D itself contains properties of type classE.

Am I right to assume that (1) means that NSKeyedArchiver will still work fine and that (2) means that using core Data may not be very simple ? I have tried to look for cases where core Data was used with complex object graph structure like my case (2) on the web but haven't found that many ressources. This is for the moment what refrains me the most from using it.

Solution

  • The two things you identify both make me lean towards using CoreData rather than NSKeyedArchiver:

    1. CoreData is well able to cope with 10,000 objects (if not considerably more), and it can support relatively straight-forward "database-like" queries of the data (sorting with NSSortDescriptors, filtering with NSPredicate). There are limitations on what can be achieved, but worst case you can load all the data into memory - which is what you would have to do with the NSKeyedArchiver solution.

      Loading in sub-second times should be achievable (I've just tested with 10,000 objects, totalling 14Mb, in 0.17 secs in the simulator), particularly if you optimise to load only essential data initially, and let CoreData's faulting process bring in the additional data when necessary. Again, this will be better than NSKeyedArchiver.

    2. Although most demos/tutorials opt for relatively straight forward data models (enough to demonstrate attributes and relationships), CoreData can cope with much more sophisticated data models. Below is a mock-up of the relationships that you describe, which took a few minutes to put together:

    Data Model

    If you generate subclasses for all those entities, then traversing those relationships is simple (both forwards and backwards - inverse relationships are managed automatically for you). Again, there are limitations (CoreData does the SQL work for you, but in so doing it is less flexible than using a relational database directly).

    Hope that helps.