I have three related tables in MySQL and a corresponding mappings in
SQLAlchemy.
It all works fine until I tried to delete objects. I tinkered with
different options but couldn't get it to work.
Here is the relevant mappings:
mapper(PlanetEntry, community_planet_tbl, properties={
}, order_by=[community_planet_tbl.c.updated.desc()])
mapper(CommunityFeed, community_feeds_tbl, properties={
'user':relation(User, backref='feeds'),
'entries':relation(PlanetEntry, backref='feed',
cascade="all, delete, delete-orphan"),
})
mapper(CommunityMember, community_members_tbl)
mapper(Community, communities_tbl, properties={
'members':relation(CommunityMember, backref='community',
cascade="all, delete, delete-orphan"),
'feeds':relation(CommunityFeed, backref='community',
cascade="all, delete, delete-orphan"),
})
I am attempting to delete a row from communities table (instance of
Communy entity) and
I get the following error:
File '/home/max/projects/site-baseline/py/lib/python2.5/site-packages/
SQLAlchemy-0.5.6-py2.5.egg/sqlalchemy/orm/unitofwork.py', line 762 in
delete_objects
task.mapper._delete_obj(task.polymorphic_todelete_objects, trans)
File '/home/max/projects/site-baseline/py/lib/python2.5/site-packages/
SQLAlchemy-0.5.6-py2.5.egg/sqlalchemy/orm/mapper.py', line 1527 in
_delete_obj
"number of objects deleted %d" % (c.rowcount, len(del_objects)))
ConcurrentModificationError: Deleted rowcount 0 does not match number
of objects deleted 1
Introspection shows that it tries to delete CommunityMember objects
with "DELETE FROM community_members WHERE
community_members.community_id = %s AND community_members.member_id =
%s"
I suspect these are already gone since there is a CASCADE rule in
community_members table in MySQL: FOREIGN KEY (`community_id`)
REFERENCES `communities` (`id`) ON DELETE CASCADE ON UPDATE CASCADE.
Why SQLAlchemy does not grok this?
If I change mapper to the following (remove cascade spec):
mapper(Community, communities_tbl, properties={
'members':relation(CommunityMember, backref='community'),
I get this:
File '/home/max/projects/site-baseline/py/lib/python2.5/site-packages/
SQLAlchemy-0.5.6-py2.5.egg/sqlalchemy/orm/sync.py', line 28 in clear
raise AssertionError("Dependency rule tried to blank-out primary key
column '%s' on instance '%s'" % (r, mapperutil.state_str(dest)))
AssertionError: Dependency rule tried to blank-out primary key column
'community_members.community_id' on instance '<CommunityMember at
0x31a0450>'
Looks correct to me. Why the original cascade clause does not work
then?
Insight is much appreciated.
Max.
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To post to this group, send email to sqlalchemy@googlegroups.com
To unsubscribe from this group, send email to
sqlalchemy+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en
-~----------~----~----~----~------~----~------~--~---
