django-pgconstraints 0.1.0

Declarative PostgreSQL constraint triggers for Django

django-pgconstraints

Declarative PostgreSQL constraint triggers for Django, with foreign-key traversal that the built-in constraints can't express.

UniqueConstraint, CheckConstraint, and GeneratedField in Django 6.0 compile down to plain PostgreSQL constraints — so they can only reference columns on the same table. django-pgconstraints provides three trigger-based classes that accept F("related__field") expressions and compile to PL/pgSQL triggers via django-pgtrigger. Their API mirrors the Django equivalents to keep the mental model familiar.

from django.db.models import F, Q
from django_pgconstraints import CheckConstraintTrigger

class OrderLine(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    quantity = models.IntegerField()

    class Meta:
        triggers = [
            CheckConstraintTrigger(
                condition=Q(quantity__lte=F("product__stock")),
                name="orderline_qty_lte_stock",
            ),
        ]

What's in the box

• UniqueConstraintTrigger — unique constraint whose fields= accepts FK chains ("book__author"). Also supports Django expressions, partial conditions, nulls_distinct, and deferred timing.
• CheckConstraintTrigger — check constraint whose Q can cross foreign keys (Q(quantity__lte=F("product__stock"))).
• GeneratedFieldTrigger — a computed column whose expression can reference related rows. The package automatically installs reverse triggers so the value stays in sync when that related data changes.

Each trigger also integrates with Django's Model.full_clean() so ORM-level validation still catches violations before they hit the database, and each accepts violation_error_code / violation_error_message so the errors raised by full_clean() match your application's error-handling conventions.

Install

pip install django-pgconstraints
# or
uv add django-pgconstraints

Add pgtrigger and django_pgconstraints to INSTALLED_APPS:

INSTALLED_APPS = [
    ...
    "pgtrigger",
    "django_pgconstraints",
    ...
]

Triggers go in Meta.triggers (a django-pgtrigger extension), not Meta.constraints. The package ships a system check (pgconstraints.E001) that flags the common mistake.

Requirements

• Python 3.14+
• Django 6.0
• PostgreSQL (any currently supported version)
• django-pgtrigger 4.17+

Documentation

Full documentation at oliverhaas.github.io/django-pgconstraints.

Runnable examples live in examples/:

• examples/simple/ — cross-publisher unique chapter names
• examples/full/ — inventory + purchase orders exercising all three triggers

License

MIT