Introducing ReactiveCoreData

Lately I’ve became seriously interested in the fantastic projects that several bright guys at GitHub open-sourced. I’m talking about ReactiveCocoa and some of its derivatives, like ReactiveCocoaLayout. If you don’t know what these are, first go and read about them. I’ll wait.

While working on UI code for Cashculator 2, I decided to utilize both of above frameworks and, so far, I’m very happy with my decision. Especially I loved how ReactiveCocoaLayout allowed me to create behaviors similar to Cocoa’s AutoLayout, which I can’t use in Cashculator for performance reasons.

Like many applications, Cashculator uses Core Data for data persistence. So I had the idea of trying to bring Core Data into the ReactiveCocoa world.

Thus, ReactiveCoreData (RCD) was born. I’ve already implemented most of the basic functionality that I wanted to include in a hypothetical 1.0. Or is it 0.1. There’s also a proof of concept demo application for the Mac, which shows only a little of how to use it.

But there are also specs which verify all the functionality, which include easy fetching, insertion, performing stuff on a background context, saving, merging. All of this in the ReactiveCocoa’s signals domain, so it looks neat and can interoperate with your other ReactiveCocoa world.

A short example:

RAC(self.filteredParents) = [[[[Parent findAll]
  where:@"name" contains:filterText options:@"cd"]
  sortBy:@"name"]
  fetchWithTrigger:objectsChanged];

This will update filteredParents property (an NSArray) to the all the Parents whose name contains text in the signal filterText (that comes from a search field, for example), sort by name and fetch.

It will fetch when either the filterText signal sends a next value or when objectsChanged signal fires (it will fire after new Parent objects were added or removed, for example).

The where: and sortBy: commands modify the NSFetchRequest that’s started with the findAll method of Parent and pass it next. Then, fetch: runs the NSFetchRequest in the current NSManagedObjectContext and sends the NSArray of the result, which gets assigned to self.filteredParents.

There’s more to ReactiveCoreData than that, but it’s a nice example.

Check ReactiveCoreData on GitHub.

I’ll be happy to get any feedback: suggestions, critique, pull requests. Use GitHub, if possible.

If you prefer to give feedback over Twitter, I’m @apparentsoft. But you better use App.net. I’m @apparentsoft over there as well.