两个带有外键的表引用另一个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? :)

Answer 1

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

Answer 2

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)