Django set relation between two models

Question

I want to save my custom Model as Field in another Model as shown below. It's normal when I create and work with them during one session. But when I start a new session Django loads the Game model with player1 and player2 that have a null id.

Here example of my code

class Player(models.Model):

    name = models.CharField(max_length=40)

class Game(models.Model):
    player1 = Player()
    player2 = Player()

Ayush Gupta · Accepted Answer · 2021-10-19T15:32:09.170

1

Seeing your comment. I think this is what you are going for.

class Player(models.Model):
    name = models.CharField(max_length=40)

class Game(models.Model):
    player1 = models.OneToOneField(Player, on_delete=models.CASCADE, related_name='p1_game')
    player2 = models.OneToOneField(Player, on_delete=models.CASCADE, related_name='p2_game')

edited Oct 19 '21 at 15:32

answered Oct 19 '21 at 15:28

Ayush Gupta

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Those related names are really bad. Name them anything that indicates you are accessing a `Game` instance! – user2390182 Oct 19 '21 at 15:31
@user2390182 How about `p1_game`? – Ayush Gupta Oct 19 '21 at 15:33
Yeah, that's much better. See my answer :) – user2390182 Oct 19 '21 at 15:34

user2390182 · Answer 2 · 2021-10-19T15:22:43.137

0

You need to create a foreign key, django's way of implementing a many-to-one relationship:

class Game(models.Model):
    player1 = models.ForeignKey(Player, on_delete=models.CASCADE, related_name="p1game")
    player2 = models.ForeignKey(Player, on_delete=models.CASCADE, related_name="p2game")

Don't forget to makemigrations and migrate!

edited Oct 19 '21 at 15:22

answered Oct 19 '21 at 14:26

user2390182

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Thanks for the answer. But I don't want to have relationships many-to-one. Also, your variant wouldn't work, because player.game_set.create() - it becomes uncertain. – Sh. Andrey Oct 19 '21 at 15:20

score 0 · Answer 3 · answered Oct 19 '21 at 14:30

0

You need to use a foreign key:

from django.contrib.gis.db import models

class Player(models.Model):
    name = models.CharField(max_length=40)

class Game(models.Model):
    player1 = models.ForeignKey(Player, on_delete=models.CASCADE)
    player2 = models.ForeignKey(Player, on_delete=models.CASCADE)

See What does on_delete do on Django models? for information about the on_delete argument.

answered Oct 19 '21 at 14:30

Fergus McClean

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Thanks for the answer. But here I would like to implement a one-to-one relationship. If it is possible. – Sh. Andrey Oct 19 '21 at 14:48
Also, this will result in clashes between player1 and player2. For example player = Player() player.game_set.create() - it become uncertain – Sh. Andrey Oct 19 '21 at 14:54
I added related names to disambiguate the reverse access. A one-to-one means that every player can be in at most two games. Once as player1 and once as player2. Is that what you are aiming for? – user2390182 Oct 19 '21 at 15:32

Django set relation between two models

3 Answers3