How do I write a Django model with ManyToMany relationsship with self through a Model

Question

I want to have a model with a ManyToMany relationship with itself, I don't know how to write this but I'l try to write some code to illustrate what I want to do.

class Person(models.Model):
   name = models.CharField()
   occupation = models.CharField()

   friends = models.ManyToManyField('self', through = PersonFriends)

My Model that I want the friends to go through

class PersonFriends(models.Model)
   ???
   comment = models.CharField()

In a ManyToMany field with through relationship if the other model's name was "Pet" for example I'd name my fields in that through class person and pet and make them models. ForeignKey(Person) and Pet for example

What to I name my fields in my PersonFriends model for the two person-fields now that they are the same model?

Answer 1

You can do something like this:

class Person(models.Model):
    name = models.CharField(max_length = 255)
    occupation = models.CharField(max_length = 255)
    friends = models.ManyToManyField('self', through = 'PersonFriends', 
          symmetrical = False)
    #     ^^^^^^^^^^^
    # This has to be false when using `through` models. Or else your 
    # model will not validate.

class PersonFriends(models.Model):
    source = models.ForeignKey(Person, related_name = 'source')
    #                                  ^^^^^^^^^^^^
    # You need different `related_name` for each when you have 
    # multiple foreign keys to the same table. 

    target = models.ForeignKey(Person, related_name = 'target')
    comment = models.CharField(max_length = 255)

Answer 2

Everything is described in the official docs for ManyToManyField.through_fields (you can search for 'recursive relationships' phrase there to quickly find what you need):

for django 1.11 you have to specify through and (!) through_fields arguments:

class Person(models.Model):
    name = models.CharField(max_length=50)

    # note the additional arguments here
    friends = models.ManyToManyField(
        'self',

        # recursive relationships to self with intermediary
        # through model are always defined as non-symmetrical
        symmetrical=False,

        through='PersonFriend',

        # this argument is required to define a custom
        # through model for many to many relationship to self
        # position matters: 1 - source (from), 2 - target (to)
        through_fields=('person', 'friend'),        
    )


class PersonFriend(models.Model):
    # required relationship-defining foreign keys
    # (note that the order does not matter, it matters
    # in 'through_fields' argument in 'friends' field of the 'Person' model)
    person = models.ForeignKey(Person, on_delete=models.CASCADE)
    friend = models.ForeignKey(Person, on_delete=models.CASCADE)

    # additional fields
    comment = models.CharField()