sync coredata with firebase in rubymotion using NSAsynchronousFetchRequest. works with large data sets. uses the cdq and motion-firebase gem.

Firebase + NSAsynchronousFetchRequest.rb

class AppDelegate
  def post_messages_firebase
    @_post_messages_firebase ||= "post_messages".fbase
  end
end

class SomeViewController < UIViewController
  def viewDidDisappear(animated=true)
    super
    adg.post_messages_firebase.removeAllObservers
  end
  def viewWillAppear(animated=true)
    super
    subscribe_to_fb
  end
  def subscribe_to_fb
    adg.post_messages_firebase.on(:added) do |snapshot|
      load_a_post_via_cd(snapshot.key.to_i,snapshot.value)
    end
    adg.post_messages_firebase.on(:changed) do |snapshot|
      load_a_post_via_cd(snapshot.key.to_i,snapshot.value)
    end
    adg.post_messages_firebase.on(:removed) do |snapshot|
      po = Post.where(id:snapshot.key.to_i)
      if po.count > 0
        po = po.first
        po.destroy
      end
    end

    #this is only called after ALL add/remove/delete events above are called
    adg.post_messages_firebase.once(:value) do |snapshot|
      :finished_inital_load.post_notification(nil)
    end
  end
  def load_a_post_via_cd(id,props,delete_me=false)
    fetchRequest = NSFetchRequest.alloc.initWithEntityName('Post')
    fetchRequest.predicate = NSPredicate.predicateWithFormat("id==%@",id)

    asyncFetch = NSAsynchronousFetchRequest.alloc.initWithFetchRequest(fetchRequest, completionBlock:lambda{|result|
      if result.finalResult.count == 0
        #ok if this method is slow; doesn't lock the main ui thread
        po = Post.find_or_create_by_id(id,withProperties:props)
      else
        po = result.finalResult.first
      end
      po.destroy if delete_me
    })
    error_ptr = Pointer.new(:object)
    cdq.contexts.all.last.executeRequest(asyncFetch,error:error_ptr)
  end
end

class Fbase
  def self.refs
    @refs ||= []
  end
  def self.ref(p)
    f = Firebase.new("https://your-name-here.firebaseio.com/#{p}")
    if !f.authenticated?
      f.authenticate('your-key-here') do |err,auth_d|
      end
    end
    Fbase.refs.push f
    f
  end
end

class String
  def fbase
    Fbase.ref self.to_s
  end
end