Multiple heads, downgrade single branch to branch point

[lafrech]

Working on two separate features concurrently, here's my migration tree:

rev1 -> rev2
     -> rev3

After upgrading to heads, current shows both rev2 (head) and rev3 (head). Fine.

Now, say I'd like to revert rev3 and keep rev2.

Downgrading to rev1 downgrades both branches. Not what I want.

I've been reading https://alembic.sqlalchemy.org/en/latest/branches.html and #464.

I didn't use branch labels but since branches can also be referred to by rev name, I tried to downgrade rev3@rev1 but it seems this downgrades both rev2 and rev3 branches. In fact, it seems anything before the @ is ignored because whatever random string I put here doesn't seem to make a difference.

Is there something I'm misunderstanding?

Is there any way to achieve what I'm trying to?

If that matters, I'm using a custom command that calls the API as

alembic.command.downgrade(config_path, "rev3@rev1")

[zzzeek]

the rev3@rev1 approach works on this end, here's an example

[classic@framework alembic:main]$ PYTHONPATH=~/dev/sqlalchemy/lib/ python -m alembic current --verbose
INFO  [alembic.runtime.migration] Context impl PostgresqlImpl.
INFO  [alembic.runtime.migration] Will assume transactional DDL.
Current revision(s) for postgresql://scott:***@localhost/test:
Rev: a815b8836ff0 (head)
Parent: 5f32c059b464
Path: /home/classic/dev/alembic/foo/versions/a815b8836ff0_rev3.py

    rev3
    
    Revision ID: a815b8836ff0
    Revises: 5f32c059b464
    Create Date: 2024-05-29 12:22:46.306333

Rev: 185d278c5837 (head)
Parent: 5f32c059b464
Path: /home/classic/dev/alembic/foo/versions/185d278c5837_rev2.py

    rev2
    
    Revision ID: 185d278c5837
    Revises: 5f32c059b464
    Create Date: 2024-05-29 12:22:04.837350

[classic@framework alembic:main]$ PYTHONPATH=~/dev/sqlalchemy/lib/ python -m alembic downgrade a815b8836ff0@5f32c059b464
INFO  [alembic.runtime.migration] Context impl PostgresqlImpl.
INFO  [alembic.runtime.migration] Will assume transactional DDL.
INFO  [alembic.runtime.migration] Running downgrade a815b8836ff0 -> 5f32c059b464, rev3
[classic@framework alembic:main]$ PYTHONPATH=~/dev/sqlalchemy/lib/ python -m alembic current --verbose
INFO  [alembic.runtime.migration] Context impl PostgresqlImpl.
INFO  [alembic.runtime.migration] Will assume transactional DDL.
Current revision(s) for postgresql://scott:***@localhost/test:
Rev: 185d278c5837 (head)
Parent: 5f32c059b464
Path: /home/classic/dev/alembic/foo/versions/185d278c5837_rev2.py

    rev2
    
    Revision ID: 185d278c5837
    Revises: 5f32c059b464
    Create Date: 2024-05-29 12:22:04.837350

[zzzeek]

make sure you are on most recent alembic, this was not always possible

[lafrech]

Oh, boy. Error on my side.

My rev3 downgrade function was copied from the rev2 migration script and because I missed a few lines while find'n replacing, the downgrade function was basically the same as the rev2 one. It triggered the same FK error as when attempting the rev2 downgrade, so I assumed it was actually performing the rev2 downgrade as well.

Thanks for confirming the method was correct and sorry about the noise.