django-pgtrigger
django-pgtrigger
helps you write Postgres triggers for your Django models.
Why should I use triggers?
Triggers can solve a variety of complex problems more reliably, performantly, and succinctly than application code. For example,
- Protecting operations on rows or columns (
pgtrigger.Protect
). - Making read-only models or fields (
pgtrigger.ReadOnly
). - Soft-deleting models (
pgtrigger.SoftDelete
). - Snapshotting and tracking model changes (django-pghistory).
- Enforcing field transitions (
pgtrigger.FSM
). - Keeping a search vector updated for full-text search (
pgtrigger.UpdateSearchVector
). - Building official interfaces (e.g. enforcing use of
User.objects.create_user
and notUser.objects.create
). - Versioning models, mirroring fields, computing unique model hashes, and the list goes on...
All of these examples require no overridden methods, no base models, and no signal handling.
Quick start
Install django-pgtrigger
with pip3 install django-pgtrigger
and add pgtrigger
to settings.INSTALLED_APPS
.
pgtrigger.Trigger
objects are added to triggers
in model Meta
. django-pgtrigger
comes with several trigger classes, such as pgtrigger.Protect
. In the following, we're protecting the model from being deleted:
import pgtrigger
class ProtectedModel(models.Model):
"""This model cannot be deleted!"""
class Meta:
triggers = [
pgtrigger.Protect(name="protect_deletes", operation=pgtrigger.Delete)
]
When migrations are created and executed, ProtectedModel
will raise an exception anytime a deletion is attempted.
Let's extend this example further and only protect deletions on inactive objects. In this example, the trigger conditionally runs when the row being deleted (the OLD
row in trigger terminology) is still active:
import pgtrigger
class ProtectedModel(models.Model):
"""Active object cannot be deleted!"""
is_active = models.BooleanField(default=True)
class Meta:
triggers = [
pgtrigger.Protect(
name="protect_deletes",
operation=pgtrigger.Delete,
condition=pgtrigger.Q(old__is_active=True)
)
]
django-pgtrigger
uses pgtrigger.Q
and pgtrigger.F
objects to conditionally execute triggers based on the OLD
and NEW
rows. Combining these Django idioms with pgtrigger.Trigger
objects can solve a wide variety of problems without ever writing SQL. Users, however, can still use raw SQL for complex cases.
Triggers are installed like other database objects. Run python manage.py makemigrations
and python manage.py migrate
to install triggers.
If triggers are new to you, don't worry. The pgtrigger docs cover triggers in more detail and provide many examples.
Compatibility
django-pgtrigger
is compatible with Python 3.8 - 3.12, Django 4.2 - 5.1, Psycopg 2 - 3, and Postgres 13 - 16.
Documentation
View the django-pgtrigger docs here to learn more about:
- Trigger basics and motivation for using triggers.
- How to use the built-in triggers and how to build custom ones.
- Installing triggers on third-party models, many-to-many fields, and other advanced scenarios.
- Writing conditional triggers.
- Ignoring triggers dynamically and deferring trigger execution.
- Multiple database, schema, and partitioning support.
- Frequently asked questions, common issues, and upgrading.
- The commands, settings, and module.
Installation
Install django-pgtrigger
with:
pip3 install django-pgtrigger
After this, add pgtrigger
to the INSTALLED_APPS
setting of your Django project.
Other Material
After you've read the docs, check out this tutorial with interactive examples from a Django meetup talk.
The DjangoCon 2021 talk also breaks down triggers and shows several examples.
Contributing Guide
For information on setting up django-pgtrigger for development and contributing changes, view CONTRIBUTING.md.
Creators
Other Contributors
- @jzmiller1
- @rrauenza
- @ralokt
- @adamchainz
- @danifus
- @kekekekule
- @peterthomassen
- @pfouque