id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
36627	Support PostgreSQL 18+ temporal constraints	Adam Johnson		"- [https://www.postgresql.org/about/news/postgresql-18-released-3142/#:~:text=PostgreSQL%2018%20adds%20temporal%20constraints Release note]
- [https://www.postgresql.org/docs/18/sql-createtable.html#SQL-CREATETABLE-PARMS-UNIQUE:~:text=If%20the%20WITHOUT%20OVERLAPS%20option `UNIQUE CONSTRAINT` docs for `WITHOUT OVERLAPS`]
- [https://www.postgresql.org/docs/18/sql-createtable.html#SQL-CREATETABLE-PARMS-UNIQUE:~:text=KEY%20%28%20column%5Fname%20%5B%2C%20%2E%2E%2E%20%5D%20%5B%2C%20column%5Fname-,WITHOUT%20OVERLAPS,-%5D%20%29%20%5B%20INCLUDE `PRIMARY KEY` docs for `WITHOUT OVERLAPS`]
- [https://www.postgresql.org/docs/18/sql-createtable.html#SQL-CREATETABLE-PARMS-UNIQUE:~:text=If%20the%20last%20column%20is%20marked%20with%20PERIOD `FOREIGN KEY` docs for `PERIOD`]

PostgreSQL 18 comes with support for ""temporal constraints"". These allow adding a special modifier to the final column in a unique constraint (`WITHOUT OVERLAPS`), primary key (`WITHOUT OVERLAPS`), or foreign key (`PERIOD`) which turns that column into a kind of ""period specifier"". This allows enforcing the given constraint is valid only for the range of that period. While the feature is not time-specific, the natural use case is to enforce uniqueness / validness over time, hence the name.

I propose that we add support for this feature in Django's `UniqueConstraint`, through some a new expression `WithoutOverlaps` in `django.contrib.postgres`, which would be used like this:

{{{
from django.db import models
from django.contrib.postgres.constraints import WithoutOverlaps
from django.contrib.postgres.fields import DateTimeRangeField

class Booking(models.Model):
    title = models.TextField()
    room = models.ForeignKey(Room, on_delete=models.CASCADE)
    span = DateTimeRangeField()
    
    class Meta:
        constraints = [
            models.UniqueConstraint(
                ""room"",
                WithoutOverlaps(""span""),
                name=""%(app_label)s_%(class)s_room_span_no_overlaps""
            ),
        ]
}}}

This could compile down to SQL like `UNIQUE (room_id, span WITHOUT OVERLAPS)`.

It may also be possible, but more tricky, to support the other two ways to specify temporal constraints:

* Primary key support would need to modify or subclass `CompositePrimaryKey` to support `WithoutOverlaps` for the final column.
* Foreign key support would need to modify or subclass `ForeignObject`, which is still a private API."	New feature	closed	contrib.postgres	dev	Normal	needsnewfeatureprocess		David Sanders	Unreviewed	0	0	0	0	0	0