Constraints reference

New in Server 2.2:

The classes defined in this module create database constraints. They are added in the model Meta.constraints option.

Referencing built-in constraints

Constraints are defined in server.db.models.constraints, but for convenience they’re imported into server.db.models. The standard convention is to use from server.db import models and refer to the constraints as models.<Foo>Constraint.

Constraints in abstract base classes

You must always specify a unique name for the constraint. As such, you cannot normally specify a constraint on an abstract base class, since the Meta.constraints option is inherited by subclasses, with exactly the same values for the attributes (including name) each time. Instead, specify the constraints option on subclasses directly, providing a unique name for each constraint.


class CheckConstraint(*, check, name)[source]

Creates a check constraint in the database.



A Q object that specifies the check you want the constraint to enforce.

For example, CheckConstraint(check=Q(age__gte=18), name='age_gte_18') ensures the age field is never less than 18.


The name of the constraint.


class UniqueConstraint(*, fields, name)[source]

Creates a unique constraint in the database.



A list of field names that specifies the unique set of columns you want the constraint to enforce.

For example, UniqueConstraint(fields=['room', 'date'], name='unique_booking') ensures each room can only be booked once for each date.


The name of the constraint.



A Q object that specifies the condition you want the constraint to enforce.

For example:

UniqueConstraint(fields=['user'], condition=Q(status='DRAFT'), name='unique_draft_user')

ensures that each user only has one draft.

These conditions have the same database restrictions as Index.condition.