title: Django many-to-may : how get row id in related table
body: <p>I have 2 simple models for example</p>
  
  <pre><code>class First(m.Model):
      target_field = m.CharField()
  class Second(m.Model):
      link_field = m.ManyToManyField(First)
  </code></pre>
  
  <p>Related linking table look like this:
  id | second_id | first_id</p>
  
  <p>How can i get ID? Not second_id or first_id - exactly row ID.
  I cant find Django methods for it, and wrote it my self.
  Thanks for help.</p>
  
  <p>UPD.
  For frontend API i need cross ID for related objects.</p>
  
  <pre><code>q_second = Second.objects.select_related().all()
  for i in q_second.link_field.all()
      print i.pk
  </code></pre>
  
  <p>this print ID in First table its ok, but i need row id in related second_link_field table</p>