title: Getting values from a Django JSONField
body: <p>I'm trying to retrieve values from a JSONField in my model, but i'm getting an error:</p>
  
  <p>'Api' object has no attribute 'openapi_spec__info__title'    </p>
  
  <pre><code>class Api(models.Model):
  ''' Model to hold infomation on the API '''
  
  # JSONB field to hold the OpenAPI spec
  openapi_spec = JSONField()
  
  # Derive product name from the OpenAPI spec, since it's a mandatory field
  def _get_product_name(self):
      return self.openapi_spec__info__title
  product_name = property(_get_product_name)
  </code></pre>
  
  <p>According to the Django docs '__' is the correct way to filter on the JSON data, but maybe it's not the correct way to access it?</p>
  
  <pre><code>{"info": {"title": "Test API", "version": "1.0.0"}}
  </code></pre>