Model definitions

We’ll use the following model definitions for our examples:

import datetime
from peewee import *
db = SqliteDatabase(':memory:')
class BaseModel(Model):
    class Meta:
        database = db
class User(BaseModel):
    username = TextField()
class Tweet(BaseModel):
    content = TextField()
    timestamp = DateTimeField(default=datetime.datetime.now)
    user = ForeignKeyField(User, backref='tweets')
class Favorite(BaseModel):
    user = ForeignKeyField(User, backref='favorites')
    tweet = ForeignKeyField(Tweet, backref='favorites')

Peewee uses ForeignKeyField to define foreign-key relationships between models. Every foreign-key field has an implied back-reference, which is exposed as a pre-filtered Select query using the provided backref attribute.

Creating test data

To follow along with the examples, let’s populate this database with some test data:

def populate_test_data():
    db.create_tables([User, Tweet, Favorite])
    data = (
        ('huey', ('meow', 'hiss', 'purr')),
        ('mickey', ('woof', 'whine')),
        ('zaizee', ()))
    for username, tweets in data:
        user = User.create(username=username)
        for tweet in tweets:
            Tweet.create(user=user, content=tweet)
    # Populate a few favorites for our users, such that:
    favorite_data = (
        ('huey', ['whine']),
        ('mickey', ['purr']),
        ('zaizee', ['meow', 'purr']))
    for username, favorites in favorite_data:
        user = User.get(User.username == username)
        for content in favorites:
            tweet = Tweet.get(Tweet.content == content)
            Favorite.create(user=user, tweet=tweet)

This gives us the following:

Attention

In the following examples we will be executing a number of queries. If you are unsure how many queries are being executed, you can add the following code, which will log all queries to the console:

import logging
logger = logging.getLogger('peewee')
logger.addHandler(logging.StreamHandler())
logger.setLevel(logging.DEBUG)

Note

In SQLite, foreign keys are not enabled by default. Most things, including the Peewee foreign-key API, will work fine, but ON DELETE behaviour will be ignored, even if you explicitly specify on_delete to your ForeignKeyField. In conjunction with the default PrimaryKeyField behaviour (where deleted record IDs can be reused), this can lead to surprising (and almost certainly unwanted) behaviour where if you delete a record in table A referenced by a foreign key in table B, and then create a new, unrelated, record in table A, the new record will end up mis-attached to the undeleted record in table B. To avoid the mis-attachment, you can use AutoIncrementField, but it may be better overall to ensure that foreign keys are enabled with pragmas=(('foreign_keys', 'on'),) when you instantiate SqliteDatabase.