[Sqlalchemy-tickets] Issue #4004: one soft delete hook to rule them all (zzzeek/sqlalchemy)

[Michael B. <iss...@bi...>]

New issue 4004: one soft delete hook to rule them all
https://bitbucket.org/zzzeek/sqlalchemy/issues/4004/one-soft-delete-hook-to-rule-them-all

Michael Bayer:

not really sure how this should look but goals are:

1. ORM keeps "delete" semantics completely.   session.delete(obj), relationships will use cascade='all, delete, delete-orphan' normally, so that everything looks like "DELETE"

2. the critical part is unitofwork.register_object().  that's where the "thing" happens that determines the "deletedness" of all objects.  unlike session.delete(), this is the place where it happens for all the relationship cascades also.

3. I am loathe to add a plain event inside of unitofwork.register_object().  at this point we are asking too much of users to understand internal flow.  before_flush() is right at the top, fine.  before_update() / before_delete(), right before the statement, OK.    But because of relationship operations that take place in dependency.py, before_flush() doesn't tell us about everything that will happen in the flush and we can't react to everything.

4. the hook is really something that happens specific to UOW - after all the presorts are done and before the actions proceed.  

register_object() hook still seems like the way to go.   this could also impact versioning recipes too.

see if a register_object() hook can come up with recipes that handle both soft_delete and versioning.  that could help come up with some way to explain it.