Is it possible to conditionally check for constraints on migrations?

[jvanasco]

I'm dealing with a database that has become quite messy due to a mix of User Error (I admit this) and sqlite3 being weird.

Then general situation is this:

• The SQLAlchemy schema incorrectly declared a UniqueConstraint(cols) when Index(cols, unique=True) should have been used.
• Not realizing this during some Alembic migrations resulted in having both UniqueConstraint and Unique Indexes with the same name on some tables.

I've been fixing undeployed migrations to avoid this from happening as the fixups are annoying.

I can't seem to find anything in the docs that would let me check the active schema to act conditionally on whether or not a constraint or index exists in the database. Is this easily possible?

Use case- On downgrades, I don't want to recreate a Unique Constraint when I should have had a Unique Index.