Alembic drops indexes for foreign keys

Question

I have a column address_id = db.Column(db.Integer, db.ForeignKey(Address.id, ondelete='CASCADE'), index=True). Autogenerating a migration with Alembic always adds a drop_index operation.

op.drop_index('address_id', 'companies')

Why does this happen every time I generate a migration?

Answer 1

This is a known bug in Alembic 0.6.1. Upgrade to 0.6.2 or newer and the problem will go away.