Add UUIDField, RangeField, JSONField, etc to database introspection

[Markus Holtermann]

django.db.backends.postgresql_psycopg2.introspection.DatabaseIntrospection.data_types_reverse does not handle UUIDField and other core or contrib.postgres specific fields. And neither does any of the other backends.

[Tim Graham]

There's an interesting question about how contrib.postgres can "contribute" introspection rules to the postgres backend. Maybe the contrib.postgres fields should be handled in a separate ticket.

[Claude Paroz]

IMHO, introspection should show the most accurate type, independently of the presence of contrib.postgres in the INSTALLED_APPS.

[Tim Graham]

Claude, the issue in my mind is adding contrib references to django/db/backends/postgresql_psycopg2/introspection.py. If we allow contrib.postgres to play by special rules, that's not very friendly to third-party apps that might wish to add introspection for their own fields. But you have more experience in this area than I do, so please give your thoughts if you had ideas on how this should work.

[Claude Paroz]

For me, this is not special rules, it's the rule "Django tries its best to introspect the database fields". If anyone want to provide contrib.mysql or contrib.oracle with custom fields, she's welcome to do so and we'll also be able to improve introspection for those backends.

Currently Django outputs models.TextField(blank=True, null=True) # This field type is a guess. for fields it doesn't know. Even if some field type is not implemented by Django models, we could imagine that we provide better hints (provided the type code is known), and point to popular third-party packages which implements those fields, inside comments.

[Tim Graham]

What I envisioned for my proposal is a way for any app to contribute a mapping to a particular database backend's DatabaseIntrospection.data_types_reverse dictionary. I guess it might work something like south.modelsinspector.add_introspection_rules does, although I haven't looked at the implementation of that. Of course there's also the need to add the appropriate import in the models file that inspectdb generates since all fields won't be in django.db.models anymore.

[Claude Paroz]

As UUIDField is a bit different (available in all backends with different implementation), I created a ​pull request just for that field.
A separate pull request will be proposed for other PostgreSQL-specific fields.

[Claude Paroz]

The "final" ​pull request, including the commit linked from the previous comment and the fix for #25454.

[Claude Paroz <claude@…>]

In 3ea7167:

Refs #24928 -- Added introspection support for UUIDField

[Claude Paroz <claude@…>]

In 0cbb6ac0:

Refs #24928 -- Added introspection support for PostgreSQL JSONField

Thanks Adam Johnson and Tim Graham for the reviews.

[Claude Paroz <claude@…>]

In a599ae60:

Refs #24928 -- Added introspection support for PostgreSQL RangeField

[Claude Paroz]

HStoreField and ArrayField support still missing.