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
36827	Adding hash index support for exclusion constraint in PostgreSQL	haki	haki	"In PostgreSQL you can’t define a unique constraint using a hash index. However, you can enforce uniqueness using an exclusion constraint and a hash index. This is useful for large values that only use equality and that are not referenced by FKs (fields like UIDs, hashes, checksums, URLs, other large texts etc.).

However, the current implementation(https://github.com/django/django/blob/4426b1a72dc289643e2ae8c190b8dc4b3a39daf7/django/contrib/postgres/constraints.py#L38) of `ExclusionConstraint` in `django.contrib.postgres.constraints` is limited to gist and spgist. It seems like the implementation haven’t changed much since it was added in 2019.

I made a local change to allow hash to the list of allowed `index_type`s and generated this constraint:

{{{
from django.contrib.postgres.constraints import ExclusionConstraint

class ShortUrl(models.Model):
    class Meta:
        constraints = (
            ExclusionConstraint(
                index_type='hash',  # <--- this index type is currently unsupported
                expressions=[
                    (F('url'), '='),
                ],
                name='%(app_label)s_url_unique_hash',
            ),
        )
}}}

It produced the expected SQL:



{{{
ALTER TABLE ""shorturl_shorturl"" ADD CONSTRAINT ""shorturl_url_unique_hash"" EXCLUDE USING hash (""url"" WITH =);
}}}


After applying the migration the constraint worked as expected."	New feature	closed	contrib.postgres	6.0	Normal	fixed		haki	Ready for checkin	1	0	0	0	0	0