title: Django model choice field - depend on other field's choice
body: <p>I need django modelform with 2 fields, where second field choice list depends on what was chosen in first one. My model:</p>
  
  <pre><code>class Offer(BaseModel):
  
      VEHICLE_TYPES = (
          ('personal','Personal car'),
          ('truck','Truck'),
      )
      vehicle_type = models.CharField(max_length=32, choices=VEHICLE_TYPES, default='personal', verbose_name='Vehicle type')
  
      PERSONAL_MAKES = (
          ('',''),
      )
      TRUCK_MAKES = (
          ('',''),
      )
      make = models.CharField(max_length=32)#what more??
  </code></pre>
  
  <p>How can I set choices of <em>make</em> field to <em>PERSONAL_MAKES</em> if vehicle_type is set to <em>personal</em>? How can I do this? Is it possible on model level?</p>