Michael Bayer wrote:
On Feb 22, 2006, at 11:47 PM, Daniel Miller wrote:
The more I think about it the more I lean toward having it removed
from the parent collection after the child is deleted (when the
session is committed, not before).
yah its just a pretty big monkeywrench to throw in...a commit()
operation currently doesnt change any datastructures at all, just writes
to the database. when you say we're going to automatically modify
collections *within* the commit, it starts to get crazy....what about
backrefs firing off, various setter/getter handlers firing off and
changing more things ? it can really blow up a commit. maybe thats
what theyre getting at with hibernate.
im really not so psyched to maintain a backwards reference of every list
an object is attached to, just so we can raise an exception when someone
goes to delete(). I was hoping to keep the whole "attributes" idea
pretty sparse since the main purpose of SA is SQL generation, not an
in-memory referential integrity engine. it would be easiest to just
check lists for deleted objects when the list itself is being saved and
throw an exception at that point, instead of against any possible list
at the point of delete. can we identify specific scenarios that might
justify the extra overhead and complexity ?
not sure if its related but i've looking for on delete and on update
actions functionality, ie. on delete cascade. i've been using a foreign
key subclass below and some db specific engine changes (attached) in
get_col_spec method (though its straight ansi afaik, though not in mysql
till 5.0), the affects of this on in memory representation of relation
collections aren't clear to me, ie. if this is a use case where such
bookkeeping would be nesc. even if its not such a case, this
functionality is something i'd like to see in sqlalchemy, as on
delete/on update fk column action specification is really helpful, i
think.
# requires corresponding database specific generator changes ( see
# attached pg sample)
class ForeignKeyWithAction( rdb.ForeignKey ):
allowed_change_actions = ( None,
'restrict',
'cascade',
'set null',
'set default', )
def __init__(self, column, on_delete=None, on_update=None):
rdb.ForeignKey.__init__( self, column )
self.on_delete = self.on_update = None
if on_delete:
assert on_delete in self.allowed_change_actions
self.on_delete = "ON DELETE %s"%on_delete
if on_update:
assert on_update in self.allowed_change_actions
self.on_update = "ON UPDATE %s"%on_update
cheers,
kapil
Index: postgres.py
===================================================================
--- postgres.py (revision 1023)
+++ postgres.py (working copy)
@@ -312,7 +312,14 @@
if column.primary_key and not override_pk:
colspec += " PRIMARY KEY"
if column.foreign_key:
- colspec += " REFERENCES %s(%s)" %
(column.column.foreign_key.column.table.fullname,
column.column.foreign_key.column.name)
+
+ colspec += " REFERENCES %s(%s)" %
(column.column.foreign_key.column.table.fullname,
column.column.foreign_key.column.name)
+
+ if hasattr(column.foreign_key, 'on_delete') and
column.foreign_key.on_delete:
+ colspec += " " + column.foreign_key.on_delete
+ if hasattr(column.foreign_key, 'on_update') and
column.foreign_key.on_update:
+ colspec += " " + column.foreign_key.on_update
+
return colspec
def visit_sequence(self, sequence):
