Modify data as part of an alembic upgrade

Question

I would like to modify some database data as part of an alembic upgrade.

I thought I could just add any code in the upgrade of my migration, but the following fails:

Answer 1

Its worth noting that if you do this, you probably want to freeze a copy of your orm model inside the migration, like this:

class MyType(Base):
  __tablename__ = 'existing_table'
  __table_args__ = {'extend_existing': True}
  id = Column(Integer, ...)
  ..

def upgrade():
  Base.metadata.bind = op.get_bind()

  for item in Session.query(MyType).all():
    ...

Otherwise you'll inevitably end up in a situation where you orm model changes and previous migrations no longer work.

Particularly note that you want to extend Base, not the base type itself (app.models.MyType) because your type might go away as some point, and once again, your migrations will fail.