Constraints referenceLink to this heading#

checkLink to this heading#

CheckConstraint.checkLink to this definition#

A Q object or boolean Expression 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.

nameLink to this heading#

CheckConstraint.nameLink to this definition#

The name of the constraint. You must always specify a unique name for the constraint.

fieldsLink to this heading#

UniqueConstraint.fieldsLink to this definition#

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.

nameLink to this heading#

UniqueConstraint.nameLink to this definition#

The name of the constraint. You must always specify a unique name for the constraint.

conditionLink to this heading#

UniqueConstraint.conditionLink to this definition#

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

Sebagai contoh:

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.

deferrableLink to this heading#

UniqueConstraint.deferrableLink to this definition#

Set this parameter to create a deferrable unique constraint. Accepted values are Deferrable.DEFERRED or Deferrable.IMMEDIATE. For example:

from django.db.models import Deferrable, UniqueConstraint

UniqueConstraint(
    name='unique_order',
    fields=['order'],
    deferrable=Deferrable.DEFERRED,
)

By default constraints are not deferred. A deferred constraint will not be enforced until the end of the transaction. An immediate constraint will be enforced immediately after every command.

includeLink to this heading#

UniqueConstraint.includeLink to this definition#

A list or tuple of the names of the fields to be included in the covering unique index as non-key columns. This allows index-only scans to be used for queries that select only included fields (include) and filter only by unique fields (fields).

Sebagai contoh:

UniqueConstraint(name='unique_booking', fields=['room', 'date'], include=['full_name'])

will allow filtering on room and date, also selecting full_name, while fetching data only from the index.

include is supported only on PostgreSQL.

Non-key columns have the same database restrictions as Index.include.

opclassesLink to this heading#

UniqueConstraint.opclassesLink to this definition#

The names of the PostgreSQL operator classes to use for this unique index. If you require a custom operator class, you must provide one for each field in the index.

Sebagai contoh:

UniqueConstraint(name='unique_username', fields=['username'], opclasses=['varchar_pattern_ops'])

creates a unique index on username using varchar_pattern_ops.

opclasses are ignored for databases besides PostgreSQL.