Fix : TypeDecorator rendering to preserve SchemaType name/schema

[khanjan2708]

Fixes Issue : sqlalchemy/sqlalchemy#13140

Description

This pull request fixes Issue sqlalchemy/sqlalchemy#13140, where sqlalchemy.Enum (and other SchemaTypes like Boolean) lost their name and schema properties when augmented with a sqlalchemy.types.TypeDecorator during autogenerated migrations.

The Fix: I have introduced a _type_repr helper in alembic/autogenerate/render.py that specifically detects TypeDecorator instances. If the implementation of the decorator is a SchemaType, Alembic now manually ensures that the name and schema attributes are preserved in the rendered migration string.

Additionally, _user_autogenerate_prefix was updated to use .get() instead of direct dictionary access to prevent KeyError regressions in certain testing environments where the full autogenerate context might not be initialized.

Checklist

This pull request is:

• A documentation / typographical error fix
  • Good to go, no issue or tests are needed
• A short code fix
  • please include the issue number, and create an issue if none exists, which
    must include a complete example of the issue. one line code fixes without an
    issue and demonstration will not be accepted.
  • Please include: Fixes: #<issue number> in the commit message
  • please include tests. one line code fixes without tests will not be accepted.
• A new feature implementation
  • please include the issue number, and create an issue if none exists, which must
    include a complete example of how the feature would look.
  • Please include: Fixes: #<issue number> in the commit message
  • please include tests.

Have a nice day!

[zzzeek]

hey there

thanks for this. however I listed out the approaches in https://github.com/sqlalchemy/alembic/issues/1551#issuecomment-2420595115 as well as another one in https://github.com/sqlalchemy/alembic/issues/1551#issuecomment-2420603412

this approach seems to use another approach, which is to get the repr string and then tries to guess how to add "name" into it, which I'd rather not do this this way. The core issue is TypeDecorator.repr is broken and item 3 in my comment at https://github.com/sqlalchemy/alembic/issues/1551#issuecomment-2420595115 is the best way to approach this.

that is, we should be changing TypeDecorator.__repr__ first and foremost. if we want to put an interim fix on the alembic side, then it should not use the TypeDecorator.__repr__ output at all and should re-implement from scratch.

most effective would be my item 3 change, which would place this on the SQLAlchemy side. ill propose that now

[zzzeek]

I'm going to fix this on the SQLAlchemy side and we no longer need this fix on the alembic side. any chance you can address the test failures on your other PR at #1793 ? that PR is stalled as it does not pass tests

[khanjan2708]

I'm going to fix this on the SQLAlchemy side and we no longer need this fix on the alembic side. any chance you can address the test failures on your other PR at #1793 ? that PR is stalled as it does not pass tests

Working on it too

[zzzeek]

hi -

the sqlalchemy fix is merged, closing this