[Sqlalchemy-tickets] Issue #3990: strange circular dependency error with only one object being changed (zzzeek/sqlalchemy)

[Adrian <iss...@bi...>]

New issue 3990: strange circular dependency error with only one object being changed
https://bitbucket.org/zzzeek/sqlalchemy/issues/3990/strange-circular-dependency-error-with

Adrian:

I have the following code: https://gist.github.com/ThiefMaster/9cea43683142912e5ffb0fa3b5d8d0a9

It fails with a circular dependency error even though there is only a change to `p` (however, both `p` and `gal` show up in
`sess.dirty` when I print it right before the commit, but `is_modified` only returns True for `p`).

It also works fine if I uncomment the expire call - but of course that's an awful workaround. `post_update=True` on the `gallery`
relationship also does the job but it seems like an SQLAlchemy bug to me since there's only one object with changes which can be flushed/committed just fine if I do
a manual expire...