PostgreSQL supports additional data integrity constraints available from the\ndjango.contrib.postgres.constraints module. They are added in the model\nMeta.constraints option.
ExclusionConstraintLink to this heading#Creates an exclusion constraint in the database. Internally, PostgreSQL\nimplements exclusion constraints using indexes. The default index type is\nGiST. To use them,\nyou need to activate the btree_gist extension on PostgreSQL.\nYou can install it using the\nBtreeGistExtension migration\noperation.
If you attempt to insert a new row that conflicts with an existing row, an\nIntegrityError is raised. Similarly, when update\nconflicts with an existing row.
Exclusion constraints are checked during the model validation.
\nnameLink to this heading#See BaseConstraint.name.
expressionsLink to this heading#An iterable of 2-tuples. The first element is an expression or string. The\nsecond element is an SQL operator represented as a string. To avoid typos, you\nmay use RangeOperators which maps the\noperators with strings. For example:
expressions = [\n ("timespan", RangeOperators.ADJACENT_TO),\n (F("room"), RangeOperators.EQUAL),\n]\nThe OpClass() expression can\nbe used to specify a custom operator class for the constraint expressions.\nFor example:
expressions = [\n (OpClass("circle", name="circle_ops"), RangeOperators.OVERLAPS),\n]\ncreates an exclusion constraint on circle using circle_ops.
index_typeLink to this heading#The index type of the constraint. Accepted values are GIST or SPGIST.\nMatching is case insensitive. If not provided, the default index type is\nGIST.
conditionLink to this heading#A Q object that specifies the condition to restrict\na constraint to a subset of rows. For example,\ncondition=Q(cancelled=False).
Kondisi ini memiliki batasan basisdata sama sebagai django.db.models.Index.condition.
deferrableLink to this heading#Set this parameter to create a deferrable exclusion constraint. Accepted values\nare Deferrable.DEFERRED or Deferrable.IMMEDIATE. For example:
from django.contrib.postgres.constraints import ExclusionConstraint\nfrom django.contrib.postgres.fields import RangeOperators\nfrom django.db.models import Deferrable\n\n\nExclusionConstraint(\n name="exclude_overlapping_deferred",\n expressions=[\n ("timespan", RangeOperators.OVERLAPS),\n ],\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\nincludeLink to this heading#A list or tuple of the names of the fields to be included in the covering\nexclusion constraint as non-key columns. This allows index-only scans to be\nused for queries that select only included fields\n(include) and filter only by indexed fields\n(expressions).
include is supported for GiST indexes. PostgreSQL 14+ also supports\ninclude for SP-GiST indexes.
violation_error_codeLink to this heading#The error code used when ValidationError is raised during\nmodel validation. Defaults to None.
violation_error_messageLink to this heading#The error message used when ValidationError is raised during\nmodel validation. Defaults to\nBaseConstraint.violation_error_message.
The following example restricts overlapping reservations in the same room, not\ntaking canceled reservations into account:
\nfrom django.contrib.postgres.constraints import ExclusionConstraint\nfrom django.contrib.postgres.fields import DateTimeRangeField, RangeOperators\nfrom django.db import models\nfrom django.db.models import Q\n\n\nclass Room(models.Model):\n number = models.IntegerField()\n\n\nclass Reservation(models.Model):\n room = models.ForeignKey("Room", on_delete=models.CASCADE)\n timespan = DateTimeRangeField()\n cancelled = models.BooleanField(default=False)\n\n class Meta:\n constraints = [\n ExclusionConstraint(\n name="exclude_overlapping_reservations",\n expressions=[\n ("timespan", RangeOperators.OVERLAPS),\n ("room", RangeOperators.EQUAL),\n ],\n condition=Q(cancelled=False),\n ),\n ]\nIn case your model defines a range using two fields, instead of the native\nPostgreSQL range types, you should write an expression that uses the equivalent\nfunction (e.g. TsTzRange()), and use the delimiters for the field. Most\noften, the delimiters will be '[)', meaning that the lower bound is\ninclusive and the upper bound is exclusive. You may use the\nRangeBoundary that provides an\nexpression mapping for the range boundaries. For example:
from django.contrib.postgres.constraints import ExclusionConstraint\nfrom django.contrib.postgres.fields import (\n DateTimeRangeField,\n RangeBoundary,\n RangeOperators,\n)\nfrom django.db import models\nfrom django.db.models import Func, Q\n\n\nclass TsTzRange(Func):\n function = "TSTZRANGE"\n output_field = DateTimeRangeField()\n\n\nclass Reservation(models.Model):\n room = models.ForeignKey("Room", on_delete=models.CASCADE)\n start = models.DateTimeField()\n end = models.DateTimeField()\n cancelled = models.BooleanField(default=False)\n\n class Meta:\n constraints = [\n ExclusionConstraint(\n name="exclude_overlapping_reservations",\n expressions=[\n (\n TsTzRange("start", "end", RangeBoundary()),\n RangeOperators.OVERLAPS,\n ),\n ("room", RangeOperators.EQUAL),\n ],\n condition=Q(cancelled=False),\n ),\n ]\n