#11964: Add the ability to use database-level CHECK CONSTRAINTS
-------------------------------------+-------------------------------------
Reporter: Matthew Schinckel | Owner: Ian Foote
Type: New feature | Status: closed
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution: fixed
Keywords: check constraint | Triage Stage: Ready for
| checkin
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Balazs Endresz):
> Is it now possible to define a field that comes with a check constraint,
or can they only be defined at the table level? I'd like to be able to
define my own StrictlyPositiveIntegerField.
Looks like positive integer fields have been already defined that way:
https://github.com/django/django/blob/084536a/django/db/models/fields/__init__.py#L637
https://github.com/django/django/blob/084536a/django/db/backends/postgresql/base.py#L95
Similarly, one can add a ''simple'' custom field (that has no additional
arguments):
{{{
class StrictlyPositiveIntegerField(models.PositiveIntegerField):
# NB the db_check method is not documented
def db_check(self, connection):
data = self.db_type_parameters(connection)
return '"%(column)s" > 0' % data
}}}
With a few tweaks it probably could be made to work with custom field args
and CheckConstraints too:
{{{
BaseDatabaseSchemaEditor.sql_create_check = (
# need to drop the check first, otherwise it can't be modified:
'ALTER TABLE %(table)s DROP CONSTRAINT IF EXISTS %(name)s'
'ALTER TABLE %(table)s ADD CONSTRAINT %(name)s CHECK (%(check)s)'
)
class CustomFieldWithArgsAndChecks(models.Field):
... # handle custom args in __init__() and deconstruct() and define
validators too
def db_check(self, connection):
constraint = models.CheckConstraint(check=models.Q(**{
f'{self.name}__gte': self.gte,
f'{self.name}__lte': self.lte,
}), name='')
with connection.schema_editor() as schema_editor:
return constraint._get_check_sql(self.model, schema_editor)
}}}
I wonder if there are any plans to officially support doing that kind of
thing in the future.
Perhaps it isn't too far out of reach now with CheckConstraints in place.
--
Ticket URL: <https://code.djangoproject.com/ticket/11964#comment:40>
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