Hi Hector,
On Fri, Nov 12, 2010 at 7:46 AM, Hector Blanco white.li...@gmail.com wrote:
Hello everyone.
I was wondering if it's possible to inherit a custom collection to
create another custom collection.
A few days ago I was trying to use my own class as a custom_collection
(http://groups.google.com/group/sqlalchemy/msg/ba1c64c3d227f586).
Thanks to Michael Bayer I was able to do it, but now I would like to
go one step further, and inherit my custom collection to create
another custom collection.
To simplify a little what I asked in the other message, let's say I have a:
def ClassA(declarativeBase):
__tablename__ = aes
id = Column(id, Integer, primary_key=True)
_whatever = Column(type, String(64))
def __init__(self):
self._whatever = whatever
Then I have my custom collection for instances of ClassA:
def ContainerOfA(dict):
__emulates__ = set
def __init__(self):
self._field = I'm a great... awesom! container
#I also defined the appender, remover and iterator
�...@collection.iterator
def __iter__(self):
return self.itervalues()
�...@collection.appender
def append(self, item):
self[item.getUniqueHash()] = item
�...@collection.remover
def remove(self, item):
if item.getUniqueHash() in self.keys():
del self[item.getUniqueHash()]
And then I was happily able to use it in any relationships:
def YetAnotherClass(declarativeBase):
id = Column(id, Integer, primary_key=True)
classesA = relationship(ClassA,
uselist=True,
secondary=intermediate_table,
collection_class=lambda: ContainerOfA(),
cascade=all, delete, delete-orphan,
single_parent=True
)
Now I needed to extend ClassA in a Class B and ContainerOfA in
ContainerOfB. I added the polymorphic stuff to ClassA and ClassB
to create a joined table inheritance, as detailed in
http://www.sqlalchemy.org/docs/orm/inheritance.html#joined-table-inheritance
. (it seems to be working fine, that's why I am not completely
detailing it here)
def ClassB(ClassA):
__tablename__ = bs #Sorry for that
__mapper_args__ = {'polymorphic_identity': 'ClassB'}
id = Column(id, Integer, ForeignKey('aes.id'), primary_key=True)
def __init__(self):
self._anotherWhatever = another whatever
def ContainerOfB(ContainerOfA):
def __init__(self):
super(ContainerOfB, self).__init__()
def anotherMethodOnlyForBInstances(self):
# do interesting stuff for B classes
Then I tried to use it in a relationship:
def YetYetAnotherClass(declarativeBase):
id = Column(id, Integer, primary_key=True)
classesB = relationship(ClassB,
uselist=True,
secondary=another_intermediate_table,
collection_class=lambda: ContainerOfB(),
cascade=all, delete, delete-orphan,
single_parent=True
)
But when I tried to append a ClassB instance through the
relationship detailed above, I got this exception:
Type ContainerOfB must elect an appender method to be a collection class
I haven't been able to replicate this behavior. When testing your
code I did notice that you are using 'def' to declare your classes,
which won't actually create the type. I make that same typo myself
periodically and it can be quite tricky to track down the one def'd
class that's causing seemingly unrelated errors.
Anyhow, I've attached the working test case I put together. If you
can modify this to replicate your behavior, we can track down any bugs
that might be present in the collection API's appender metadata
bookkeeping. You definitely should not have to re-declare an
@appender on a subclass- the collection mechanics should be sweeping
over your inherited class and transparently picking up the methods.
This is definitely working for the cases in the SQLA unit tests, but
it's definitely possible you've found some corner case with that dict
that's declared to be emulating a set.
Cheers,
Jason
I thought... ok, ok... let's just explicitly add the 'appender' to
the ContainerOfB class... The only thing I need to do is calling the
appender of the super class, anyway... no biggie and so I did:
def ContainerOfB(ContainerOfA):
# [ . . . ] #
�...@collection.appender
def append(self, classBInstance):
return super(ContainerOfB, self).append(classBInstance)
But then... another exception when I tried to add an instance of ClassB():
InvalidRequestError: Instance ClassB at 0xba9726c is already associated
with an instance of class 'mylibraries.classesTest.YetYetAnotherClass'
via its YetYetAnotherClass.classesB attribute, and is only allowed a single
parent.
Well... I need
