The classes defined in this module create database constraints. They are added\nin the model Meta.constraints\noption.
CheckConstraintLink to this heading#Creates a check constraint in the database.
\ncheckLink to this heading#A Q object or boolean Expression that\nspecifies the check you want the constraint to enforce.
For example, CheckConstraint(check=Q(age__gte=18), name='age_gte_18')\nensures the age field is never less than 18.
nameLink to this heading#The name of the constraint. You must always specify a unique name for the\nconstraint.
\nUniqueConstraintLink to this heading#Creates a unique constraint in the database.
\nexpressionsLink to this heading#Positional argument *expressions allows creating functional unique\nconstraints on expressions and database functions.
例:
\nUniqueConstraint(Lower('name').desc(), 'category', name='unique_lower_name_category')\ncreates a unique constraint on the lowercased value of the name field in\ndescending order and the category field in the default ascending order.
Functional unique constraints have the same database restrictions as\nIndex.expressions.
fieldsLink to this heading#A list of field names that specifies the unique set of columns you want the\nconstraint to enforce.
\nFor example, UniqueConstraint(fields=['room', 'date'],\nname='unique_booking') ensures each room can only be booked once for each\ndate.
nameLink to this heading#The name of the constraint. You must always specify a unique name for the\nconstraint.
\nconditionLink to this heading#A Q object that specifies the condition you want the constraint to\nenforce.
例:
\nUniqueConstraint(fields=['user'], condition=Q(status='DRAFT'), name='unique_draft_user')\nensures that each user only has one draft.
\nThese conditions have the same database restrictions as\nIndex.condition.
deferrableLink to this heading#Set this parameter to create a deferrable unique constraint. Accepted values\nare Deferrable.DEFERRED or Deferrable.IMMEDIATE. For example:
from django.db.models import Deferrable, UniqueConstraint\n\nUniqueConstraint(\n name='unique_order',\n fields=['order'],\n deferrable=Deferrable.DEFERRED,\n)\nBy default constraints are not deferred. A deferred constraint will not be\nenforced until the end of the transaction. An immediate constraint will be\nenforced immediately after every command.
\n\n\nincludeLink to this heading#A list or tuple of the names of the fields to be included in the covering\nunique index as non-key columns. This allows index-only scans to be used for\nqueries that select only included fields (include)\nand filter only by unique fields (fields).
例:
\nUniqueConstraint(name='unique_booking', fields=['room', 'date'], include=['full_name'])\nwill allow filtering on room and date, also selecting full_name,\nwhile 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#The names of the PostgreSQL operator classes to use for\nthis unique index. If you require a custom operator class, you must provide one\nfor each field in the index.
\n例:
\nUniqueConstraint(name='unique_username', fields=['username'], opclasses=['varchar_pattern_ops'])\ncreates a unique index on username using varchar_pattern_ops.
opclasses are ignored for databases besides PostgreSQL.