Two tables with foreign key referencing the other, NameError

Question

I'm trying to create tables with foreign keys in database with peewee.
Player table has ForeignKey to Team table and Team table has ForeignKey to Player table. When i run my code i'm getting NameError: name 'Team' is not defined
Here is my code:

class Player(Model):
    nickname = CharField(max_length=30)
    steam_id = CharField(max_length=15)
    team = ForeignKeyField(Team)
    class Meta:
        database = db

class Team(Model):
    name = CharField(max_length=30)
    captain = ForeignKeyField(Player)
    class Meta:
        database = db
Player.create_table()
Team.create_table()

Can someone help me? :)

I don't know peewee ònly SQL but you can't set a FK to a "class" / table that doesn't exists in SQL. I think here it's the same. You could try to add the FK after creation of both classes. Beside of this you could do a class `TeamPlayer` where you got 3 attributes: Player, Team and captain. So you avoid the crossing FKs — bish, Jan 16 '15 at 15:21
Thanks for your fast answer! `setattr(Team, "captain", ForeignKeyField(Player))`, `setattr(Player, "team", ForeignKeyField(Team))` fixed the problem :) — KsaneK, Jan 16 '15 at 15:32
This approach is actually not going to work well because of certain hooks that run during metaclass / model class creation. If you want to add a field dynamically instead you should call "field.add_to_class(model_class, field_name)". This will take care of setting the attribute correctly and running the hooks. *The best / correct answer*, however, is listed below in the answers section. — coleifer, Jan 16 '15 at 19:30

score 0 · Accepted Answer · answered Jan 16 '15 at 16:14

You're getting this error because you are referencing Team in Player, before you have defined Team. You have a circular dependency here. Team is dependent on Player and Player is dependent on Team.

My first suggestion would be to drop one of the dependencies. Do you really need a reference to the other in both tables?

If you do, then the peewee docs has an entire section dedicated to handling this situation: http://peewee.readthedocs.org/en/latest/peewee/models.html#circular-foreign-key-dependencies

This isn't an answer, its a link to an answer. – Shayne Feb 22 '19 at 08:33 — Shayne, Feb 22 '19 at 08:33

score 0 · Answer 2 · answered Feb 22 '19 at 08:36

You need to use DeferredForeignKey this uses the Django style type-as-string approach, but comes with the caveat it won't create your database constraints for you

So for

team = ForeignKeyField(Team)

use

team = DeferredForeignKeyField('Team')

and then later

db.create_tables([Player,Team])
Player._schema.create_foreign_key(Player.team)

Two tables with foreign key referencing the other, NameError

2 Answers2