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
33607	PostgresIndex.create_sql() doesn't respect the using argument.	Alexandru Mărășteanu	Alexandru Mărășteanu	"`django.contrib.postgres.indexes.PostgresIndex` uses the `suffix` attribute for both generating the index name (in `Index.set_name_with_model` see https://github.com/django/django/blob/fac662f4798f7e4e0ed9be6b4fb4a87a80810a68/django/db/models/indexes.py#L153-L186) and for deciding the indexing method (in `PostgresIndex.create_sql` i.e. `CREATE INDEX ... USING {suffix} ...` see https://github.com/django/django/blob/fac662f4798f7e4e0ed9be6b4fb4a87a80810a68/django/contrib/postgres/indexes.py#L25-L36). A developer using and extending `PostgresIndex` for use with multiple opclasses is unable to specify a custom suffix for the naming scheme.

For example, given two custom indexes like:


{{{
class Foo(GinIndex):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, opclasses=[some opclass], **kwargs)


class Bar(GinIndex):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, opclasses=[some opclass], **kwargs)
}}}


If set on the same model fields, both `Foo.set_name_with_model` and `Bar.set_name_with_model` would then generate the same index name à la `dbtable_field_hash_gin` which is not ok because index names need to be unique.

Setting custom `suffix`es on `Foo` and `Bar` is not possible with the current code because `PostgresIndex.create_sql` uses the suffix as the index method. If the suffix doesn't match any of the supported opclasses, then PostgreSQL complains about it.

To workaround that, an option would be to override the `create_sql` method:

{{{
class Foo(GinIndex):
    suffix = ""foo""
    
    def __init__(self, *args, **kwargs):
        super().__init__(*args, opclasses=[some opclass], **kwargs)

    def create_sql(self, model, schema_editor, using="""", **kwargs):
        return super().create_sql(model, schema_editor, using=""gin"", **kwargs)


class Bar(GinIndex):
    suffix = ""bar""

    def __init__(self, *args, **kwargs):
        super().__init__(*args, opclasses=[some opclass], **kwargs)

    def create_sql(self, model, schema_editor, using="""", **kwargs):
        return super().create_sql(model, schema_editor, using=""gin"", **kwargs)
}}}

The problem is, even though `PostgresIndex.create_sql` accepts a `using` argument, it currently ignores it. From the source code:

{{{
class PostgresIndex(Index):
    ...

    def create_sql(self, model, schema_editor, using="""", **kwargs):
        ...
        statement = super().create_sql(
            model, schema_editor, using="" USING %s"" % self.suffix, **kwargs
        )
        ...
}}}

So in the end there's no way to extend the `PostgresIndex` with a custom suffix. I was able to do it by temporarily setting a custom suffix in `set_name_with_model` but that's more of a hack rather than a solution.

--

That said, I believe there are two things which need to be addressed here:

1. Distinguish between the index name suffix and the index method

`PostgresIndex` would then declare another property which indicated the method to use when defining the index i.e. `using`.

2. `PostgresIndex.create_sql` respects the `using` argument

E.g. (also considering point 1 above):

{{{
class PostgresIndex(Index):
    ...

    def create_sql(self, model, schema_editor, using="""", **kwargs):
        ...
        statement = super().create_sql(
            model, schema_editor, using=using or self.using, **kwargs
        )
        ...
}}}

---

If this is accepted, I'm available to work on it."	Cleanup/optimization	closed	contrib.postgres	dev	Normal	fixed			Ready for checkin	0	0	0	0	1	0