is there a way to set peewee fields via a mixin?

Question

I'm trying to set up a reusable set of data models which I can include in multiple apps, something like this (I'm using users as an example here, but the actual one is a peewee backend for the Authlib library):

# mixins.py

class UserMixin(peewee.Model):
    username = peewee.CharField()
    password = peewee.CharField()

    def set_password(self):
        # do stuff
    ...

Once that mixin's created, I should be able to import it like this, defining only the additional fields (the defaults will already be there from the mixin)

# models.py

db = peewee.SqliteDatabase(config.get('DATABASE_FILE'))

class BaseModel(peewee.model):
    class Meta:
        database = db

class User(BaseModel, UserMixin):
    email = peewee.CharField()
    ...

I've seen people do this with SQLAlchemy, but when I use this strategy with peewee it doesn't seem to save the fields properly:

• if UserMixin inherits from peewee.Model, it says "unable to resolve import hierarchy" (probably since we're importing from peewee.Model multiple times)
• if UserMixin is just an object, then peewee doesn't seem to handle its fields properly: they all end up as unbound instances and don't get saved in the database.

My question: is there an "official way" to create reusable model mixins with fields in peewee?

I've seen other projects (such as flask-login) use mixins, but those are generally additional functions like set_password in this example, and not ones that define the fields themselves.

---

I have a few potential alternate solutions, like

• Define the models themselves, rather than mixins, in the shared file, and override their .Meta.database separately for each models.py entry
• Define only the other functions in the mixin; let the fields be defined separately each time in models.py
• Use the shared code as a file to copy-paste from rather than importing directly.

But there's probably some cleaner way of doing this?

Answer 1

Here's a simple example:

from peewee import *

db = SqliteDatabase(':memory:')

class Base(Model):
    class Meta:
        database = db


class UserModelMixin(Model):
    username = TextField()

class User(UserModelMixin, Base):
    pass

print(User._meta.fields)
#{'id': <AutoField: User.id>, 'username': <TextField: User.username>}

I think the problem was the ordering of your mixins.