On Jul 8, 2011, at 5:28 PM, Kent wrote: > Suppose I have a related collection that is *not* single_parent and > *not* cascade delete or delete_orphan. (The reasons are poor > relational schema design, which I can't control.) > > I would like to programatically delete records occasionally, but > session.delete(instance) throws "AssertionError: Dependency rule tried > to blank-out primary key column". > > Because this is not single_parent, I do not want delete_orphan True. > > How can I accomplish deleting this instance?
So "dependency rule tried to blank out PK column" is one of those errors where if SQLAlchemy left it out, you'd get an error at the SQL level instead (assuming SQLA still nulls out the value). Usually we just go for that behavior, but for that error at some early point I felt we needed to say to the user, no really, what you're doing here means you're going to set a PK to NULL, we thought we'd might tell you sooner. If you have an object that relates to its parent via a foreign key that's on its PK, hmm OK if that PK is composite then it could be a collection. The question would be what do you want to do with that child collection object, if not delete it ? If the parent is ID=5 and the child object has composite PK (5, "foo") where the "5" is a foreign key, are you saying "5" refers to some other row somewhere also ? I might need to see how you are relating the rows in this case. Assuming you're not using standard relational PK/FK types of rules though it may be just a matter of setting passive_deletes="all" which is designed for the "please don't touch the related column" use case. Perhaps I rambled on too long without just saying that, as we added that for those weird cases where folks wanted the child row to remain unaffected. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
