title: How to create Prefetch queryset based on parent queryset in django
body: <p>Here is the scenario, a project model which contains multiple bids.</p>
  
  <pre><code>Class Project(models.Model):
      user = models.ForeignKey()
  
  Class Bid(models.Model):
      project = models.ForeignKey(Project, related_name='bids')
  </code></pre>
  
  <p>When we are querying projects, we want to prefetch bids for projects.</p>
  
  <pre><code>Project.objects.filter(whatever condition).prefetch_related(
       Prefetch('bids', queryset=Bid.objects.all())
  )
  </code></pre>
  
  <p>Here we only want to fetch the bids that belongs to the filtered projects, but not all the bids, how can we specify that?  I am expecting something like </p>
  
  <pre><code>queryset=Bid.objects.filter(project=project?)... 
  </code></pre>
  
  <p>Thanks.</p>