I am creating a Collection class using the OrderedDict and
MappedCollection with primary key id as the key index. The problem,
as noted in the docs, is that the key should be an immutable field.
Since I am using a primary key, the value will change when I am
instantiating a new object and adding it to the collection. The code
illustrates my concept:
class Collection(OrderedDict, MappedCollection):
def __init__(self, *args, **kwargs):
MappedCollection.__init__(self, keyfunc=lambda item: item.id)
OrderedDict.__init__(self, *args, **kwargs)
def refresh(self, *args, **kwargs):
""" Updates all keys based on the keyfunc and each current
value"""
dict_copy = self.copy()
self.clear()
for item in dict_copy.values():
MappedCollection.set(self, item)
class Parent(Base): pass
class Child(Base): pass
session.mapper(class_=Child, local_table=child_table)
session.mapper(class_=Parent, local_table=parent_table,
properties={'childs':relation(Child, backref='parent',
collection_class=ChildCollection)})
some_collection = ChildCollection()
new_child = Child(id=None, data='foo')
some_collection.set(new_child) # key is None, id is None
session.save(some_collection.values()) # save the child
# at this point, key is still None, but id is 1
some_collection.refresh() # key will be 1.
# I would like the refresh behavior to be invoked during/after a
flush.
Now, if I saved the Child under the Parent, then the key index would
have been updated automatically like so:
my_parent = Parent
Parent.childs.set(new_child)
session.save(Parent)
# The childs index will be 1
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