CODEWITHSUNDEEP
pythondjangodjango-modelsmany-to-many
Vyas Rao
Vyas Rao

Reputation: 498

Access many-to-many related to the same model

I have a movie database with has following models. I store the director details in Actor model itself. That is I create an actor and then link him as director. Through this I can get the director who is also an actor. Now my problem is to list all the directors. I am not able write the query. I get ReverseManyRelatedObjectsDescriptor most of the time.

class Actor(models.Model):
    actorid = models.AutoField(primary_key=True)
    name = models.CharField(max_length=250)
    sex = models.CharField(max_length=1)

    def director_list(self):
        directors = self.filter(actor__in=Movie.director).distinct()
                        **#ReverseManyRelatedObjectsDescriptor error**
        return directors


class Movie(models.Model):
    movieid = models.AutoField(primary_key=True)
    title = models.CharField(max_length=250)
    actor = models.ManyToManyField(Actor, related_name="actor")
    director= models.ManyToManyField(Actor, related_name="director")

Please help, thanks in advance.

Upvotes: 0

Views: 96

Answers (1)

xecgr
xecgr

Reputation: 5193

If I understood well your question, your need those actors who are directors (without a specific movie). So what I'd done is create a class method of Actor, like this:

class Actor(models.Model):
    actorid = models.AutoField(primary_key=True)
    name = models.CharField(max_length=250)
    sex = models.CharField(max_length=1)

    @classmethod
    def director_list(cls):

        directors_available  = set (
            d.actorid
            for movie in Movie.objects.filter(director__is_null = False)
            for d in movie.director.all()
        )
        actors_directors     = Actor.objects.filter(actorid__in = list(directors_available))

        return actors_directors

And now you can get all directors that are actors like this:

director_list = Actor.director_list()

Upvotes: 1

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