As of Django 2.2, you can add database constraints to your models. I find database constraints extremely valuable and one of those few features that Django really needed.
This blog post is more of a quick reference for myself when adding constraints to my Django models
Django has support for both
UniqueConstraints. You'll need to add your constraints to your models
Meta.constraints like below.
CheckConstaints you're required to provide the
check and the
name of the constraint. The
check kwarg on the
CheckConstraint is where you'll put your database constraint. When you're creating your
check you'll want to use the
Q object to specify the check. The syntax for the constraint in the
Q object is similar to the syntax you would use when building a django query.
In our example above the
CheckConstraint will ensure no object will be created in your datbase table that has less than 2 doors.
UniqueConstraint is similar to the
CheckConstraint but here you'll add conditions against fields to ensure their uniquness. This gives you a little more flexibility than using the
unique keyword on a model field or with
unique_together. This constraint allows you to add conditionals to generate uniqueness within your database table.
When adding a
UniqueConstraint you'll need to add a list of
fields that apply to the constraint, your
condition and the
name of the constraint. A very simple example is ensuring something only has a single "active" record.