Batasan basisdata spesifik PostgreSQLLink to this heading
PostgreSQL supports additional data integrity constraints available from the
django.contrib.postgres.constraints module. They are added in the model
Meta.constraints option.
ExclusionConstraintLink to this heading
- class ExclusionConstraint(*, name, expressions, index_type=None, condition=None)Link to this definition
Creates an exclusion constraint in the database. Internally, PostgreSQL implements exclusion constraints using indexes. The default index type is GiST. To use them, you need to activate the btree_gist extension on PostgreSQL. You can install it using the
BtreeGistExtensionmigration operation.If you attempt to insert a new row that conflicts with an existing row, an
IntegrityErroris raised. Similarly, when update conflicts with an existing row.
nameLink to this heading
- ExclusionConstraint.nameLink to this definition
Nama dari batasan.
expressionsLink to this heading
- ExclusionConstraint.expressionsLink to this definition
An iterable of 2-tuples. The first element is an expression or string. The
second element is an SQL operator represented as a string. To avoid typos, you
may use RangeOperators which maps the
operators with strings. For example:
expressions=[
('timespan', RangeOperators.ADJACENT_TO),
(F('room'), RangeOperators.EQUAL),
]
index_typeLink to this heading
- ExclusionConstraint.index_typeLink to this definition
The index type of the constraint. Accepted values are GIST or SPGIST.
Matching is case insensitive. If not provided, the default index type is
GIST.
conditionLink to this heading
- ExclusionConstraint.conditionLink to this definition
A Q object that specifies the condition to restrict
a constraint to a subset of rows. For example,
condition=Q(cancelled=False).
Kondisi ini memiliki batasan basisdata sama sebagai django.db.models.Index.condition.
ContohLink to this heading
The following example restricts overlapping reservations in the same room, not taking canceled reservations into account:
from django.contrib.postgres.constraints import ExclusionConstraint
from django.contrib.postgres.fields import DateTimeRangeField, RangeOperators
from django.db import models
from django.db.models import Q
class Room(models.Model):
number = models.IntegerField()
class Reservation(models.Model):
room = models.ForeignKey('Room', on_delete=models.CASCADE)
timespan = DateTimeRangeField()
cancelled = models.BooleanField(default=False)
class Meta:
constraints = [
ExclusionConstraint(
name='exclude_overlapping_reservations',
expressions=[
('timespan', RangeOperators.OVERLAPS),
('room', RangeOperators.EQUAL),
],
condition=Q(cancelled=False),
),
]
In case your model defines a range using two fields, instead of the native
PostgreSQL range types, you should write an expression that uses the equivalent
function (e.g. TsTzRange()), and use the delimiters for the field. Most
often, the delimiters will be '[)', meaning that the lower bound is
inclusive and the upper bound is exclusive. You may use the
RangeBoundary that provides an
expression mapping for the range boundaries. For example:
from django.contrib.postgres.constraints import ExclusionConstraint
from django.contrib.postgres.fields import (
DateTimeRangeField,
RangeBoundary,
RangeOperators,
)
from django.db import models
from django.db.models import Func, Q
class TsTzRange(Func):
function = 'TSTZRANGE'
output_field = DateTimeRangeField()
class Reservation(models.Model):
room = models.ForeignKey('Room', on_delete=models.CASCADE)
start = models.DateTimeField()
end = models.DateTimeField()
cancelled = models.BooleanField(default=False)
class Meta:
constraints = [
ExclusionConstraint(
name='exclude_overlapping_reservations',
expressions=(
(TsTzRange('start', 'end', RangeBoundary()), RangeOperators.OVERLAPS),
('room', RangeOperators.EQUAL),
),
condition=Q(cancelled=False),
),
]