The unofficial Django swappable models API.
Django Swappable Models - No longer only for auth.User!
Swapper is an unofficial API for the undocumented but very powerful Django feature: swappable models. Swapper facilitates implementing arbitrary swappable models in your own reusable apps.
Example Use Case
Suppose your reusable app has two related tables:
from django.db import models class Parent(models.Model): name = models.TextField() class Child(models.Model): name = models.TextField() parent = models.ForeignKey(Parent)
Suppose further that you want to allow the user to subclass either or both of these models and supplement them with their own implementations. You could use Abstract classes (e.g. BaseParent and BaseChild) for this, but then you would either need to:
- Avoid putting the foreign key on BaseChild and tell the user they need to do it.
- Put the foreign key on BaseChild, but make Parent a concrete model that can’t be swapped
- Use swappable models, together with ForeignKeys that read the swappable settings.
This third approach is taken by Django to facilitate swapping of the auth User model. Swapper extends this approach to apply to any model.
pip install swapper
Extending the above example, create abstract base classes and default implementations:
# reusableapp/models.py from django.db import models from swapper import swappable_setting, get_model_name class BaseParent(models.Model): # minimal base implementation ... class Meta: abstract = True class Parent(BaseParent): # default (swappable) implementation ... class Meta: swappable = swappable_setting('reusableapp', 'Parent') class BaseChild(models.Model): parent = models.ForeignKey(get_model_name('reusableapp', 'Parent')) # minimal base implementation ... class Meta: abstract = True class Child(BaseChild): # default (swappable) implementation ... class Meta: swappable = swappable_setting('reusableapp', 'BaseChild')
Then the user can override one or both models in their own app:
# myapp/models.py from reusableapp.models import BaseParent class Parent(BaseParent): # custom implementation ...
The user then specifies the appropriate setting to trigger the swap:
# myproject/settings.py REUSABLEAPP_PARENT_MODEL = "myapp.Parent"
Note: Instead of importing concrete models directly, always use the swapper: ```python # reusableapp/views.py
Might work, might not
from .models import Parent
from swapper import load_model Parent = load_model(“reusableapp”, “Parent”) Child = load_model(“reusableapp”, “Parent”)
def view(request, *args, **kwargs): qs = Parent.objects.all() # …