django-pgtrigger ################

django-pgtrigger helps you write Postgres triggers <https://www.postgresql.org/docs/current/sql-createtrigger.html>__ for your Django models. It is compatible with Python 3.7 to 3.10 and Django 2.2 to 4.1.

Why should I use triggers?

Triggers can solve a variety of complex problems much more reliably and succinctly than application code. For example,

1. Protecting operations on rows or columns (pgtrigger.Protect).
2. Soft-deleting models (pgtrigger.SoftDelete).
3. Snapshotting and tracking model changes (django-pghistory <https://django-pghistory.readthedocs.io/>__).
4. Enforcing field transitions (pgtrigger.FSM).
5. Keeping a search vector updated for full-text search (pgtrigger.UpdateSearchVector).
6. Building official interfaces (e.g. enforcing use of User.objects.create_user and not User.objects.create).
7. 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:

.. code-block:: python

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 internal database error anytime someone tries to delete it.

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:

.. code-block:: python

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 fret. The pgtrigger docs <https://django-pgtrigger.readthedocs.io/>__ break down the core components of a trigger in the tutorial. They also provide many more examples.

Documentation

View the pgtrigger docs here <https://django-pgtrigger.readthedocs.io/>__

Other Material

After you've read the docs, check out this tutorial <https://wesleykendall.github.io/django-pgtrigger-tutorial/>__ with interactive examples from a Django meetup talk.

The DjangoCon 2021 talk <https://www.youtube.com/watch?v=Tte3d4JjxCk>__ also breaks down triggers and shows several examples.

Installation

Install django-pgtrigger with::

pip3 install django-pgtrigger

After this, add pgtrigger to the INSTALLED_APPS setting of your Django project.

Contributing Guide

For information on setting up django-pgtrigger for development and contributing changes, view CONTRIBUTING.rst <CONTRIBUTING.rst>_.

Primary Authors

• @wesleykendall (Wes Kendall, [email protected])

Other Contributors

• @jzmiller1
• @rrauenza
• @ralokt