How to query all model objects except the ones that already are in another model?-CodePudding

I am working on a Django application. I have 2 models relevant to the question:

class Quiz(models.Model):
  """
  Represents a Quiz for a `Module`.

  It will have a `name`
  """
  name = models.CharField(max_length=200)
  user = models.ManyToManyField('cme.Bussines', related_name='quizes', through='UserQuiz', through_fields=('quiz', 'user'))

  def __str__(self) -> str:
    return f'{self.name}'

class Trio(models.Model):
  """
  Represents the content for a Module.  

  Each `Trio` will have, as it's name says, 3 content fields, plus the
  `Module` it belongs to.

  It will have a `file`, a `video` (which will be a URL to a YT video), and a `quiz`
  (which will be key to `Quiz`)
  """
  file = models.FileField(upload_to='legacy/classes/', max_length=254)
  quiz = models.ForeignKey(Quiz, on_delete=models.SET_NULL, related_name='trios', null=True, blank=True)
  video = models.URLField()
  module = models.ForeignKey(Module, on_delete=models.CASCADE, related_name='trios')
  user = models.ManyToManyField('cme.Bussines', related_name='trios', through='UserTrio', through_fields=('trio', 'user'))

  def __str__(self) -> str:
    return f'Trio {self.id} de {self.module}'

I want to query all the Quizzes that are not in quiz field of Trio. Is there a way of doing this?

CodePudding user response：

Yes, you can query with:

Quiz.objects.filter(trios=None)

This will make a LEFT OUTER JOIN and only retain Quizzes for which there is no related Trio object.

CodePudding user response：

You can query all Quiz objects whose id is seen in any Trio object :

Quiz.objects.exclude(id__in=Trio.objects.values("quiz_id"))

You can also refine the query further. For example, let's say you want all Quiz objects not referred by a specific subset of Trio objects, you can do so by adding a filter in your exclude expression, something like :

Quiz.objects.exclude(id__in=Trio.objects.filter(...).values("quiz_id"))