title: Django Set Default as Subset of ManyToMany Model Field
body: <pre><code>class UserProfile(models.Model):
      project_assignments =  models.ManyToManyField('drawingManager.Project', default=SetDefaultProject(self,default_assignment))
      user =  models.OneToOneField(User)
      default_project
  
      def SetDefaultProject(self,default_assignment):
          if default_assignment:
              self.default_project = default_assignment
          else:
              self.default_project = #somehow choose newest project
  
      def __unicode__(self):
          admin_reference = self.user.first_name + self.user.last_name
          return admin_reference
  </code></pre>
  
  <p>I'm trying to achieve the following behavior.  When a user is added at least one project assignment is set at the default.  And they can later, through an options interface set their default to any of the subset of project_assignments.  But it's not clear to me when you can use Foreign Key and Many to Many Fields as just python code and when you can't.</p>