blerg.js

function randomDeck(player, n) {
  var store = player.store;
  var deck = player.get('deck');
  var r, promises = [];
  
  return store.findAll('card')
    .then(function(cards){
      var lastIndex = cards.get('length') - 1;
      for(var i = 0; i < n; i++) {
        r = randomInt(lastIndex);
        var card = cards.objectAt(r);
        var promise = store.createRecord('deck-card', {
          card: card,
          player: player
        }).save();

        promises.push(promise);
      }

      return player.save();
    })
    .then(function(){
      return Ember.RSVP.all(promises);
    });
  });
}