title: Factory Boy and related objects creation
body: <p>Let's say you have these Django models related this way:</p>
  
  <pre><code>class Service:
     restaurant = models.ForeignKey(Restaurant)
     hist_day_period = models.ForeignKey(DayPeriod)
  
  class DayPeriod:
     restaurant = models.ForeignKey(Restaurant)
  </code></pre>
  
  <p>I want to create a <code>Service</code> object, using a Factory. It should create all 3 models but use the <strong>same</strong> restaurant.</p>
  
  <p>Using this code:</p>
  
  <pre><code>class ServiceFactory(factory.django.DjangoModelFactory):
      class Meta:
          model = Service
  
      restaurant = factory.SubFactory('restaurants.factories.RestaurantFactory')
  
      hist_day_period = factory.SubFactory(
          'day_periods.factories.DayPeriodFactory', restaurant=restaurant)
  </code></pre>
  
  <p>Factory boy will create 2 different restaurants:</p>
  
  <pre><code>s1 = ServiceFactory.create()
  s1.restaurant == s1.hist_day_period.restaurant
  &gt;&gt;&gt; False
  </code></pre>
  
  <p>Any idea on how to do this? It's unclear to me if I should use <code>related factors</code> instead of <code>SubFactory</code> to accomplish this.</p>