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    <p>You have to define your own collection class. There are only 3 methods to implement: appender, remover, and converter. See <code>sqlalchemy.orm.collections.MappedCollection</code> as an example.</p> <p><strong>Update:</strong> Here is quick-n-dirty implementation according to your requirements:</p> <pre><code>from sqlalchemy import * from sqlalchemy.orm import mapper, relation, sessionmaker from sqlalchemy.orm.collections import collection metadata = MetaData() parent = Table('parent', metadata, Column('parent_id', Integer, primary_key=True), Column('name', Unicode), ) child = Table('child', metadata, Column('child_id', Integer, primary_key=True), Column('name', Unicode), ) parent_child = Table('parent_child', metadata, Column('parent_id', Integer, ForeignKey(parent.c.parent_id)), Column('child_id', Integer, ForeignKey(child.c.child_id)), Column('number', Integer), PrimaryKeyConstraint('parent_id', 'child_id'), ) class ParentChild(object): def __init__(self, child, number): self.child = child self.number = number class Parent(object): pass class Child(object): pass class MyMappedCollection(object): def __init__(self, data=None): self._data = data or {} @collection.appender def _append(self, parent_child): l = self._data.setdefault(parent_child.number, []) l.append(parent_child) def __setitem__(self, number, child): self._append(ParentChild(number=number, child=child)) def __getitem__(self, number): return tuple(pc.child for pc in self._data[number]) @collection.remover def _remove(self, parent_child): self._data[parent_child.number].remove(parent_child) @collection.iterator def _iterator(self): for pcs in self._data.itervalues(): for pc in pcs: yield pc def __repr__(self): return '%s(%r)' % (type(self).__name__, self._data) mapper(Parent, parent, properties={ 'children': relation(ParentChild, collection_class=MyMappedCollection), }) mapper(Child, child) mapper(ParentChild, parent_child, properties={ 'parent': relation(Parent), 'child': relation(Child), }) engine = create_engine('sqlite://') db = sessionmaker(bind=engine)() metadata.create_all(bind=engine) p = Parent() c1 = Child() c2 = Child() c3 = Child() p.children[1] = c1 p.children[1] = c2 p.children[2] = c3 db.add(p) db.commit() p_id = p.parent_id db.expunge_all() p = db.query(Parent).get(p_id) print p.children[1] print p.children[2] </code></pre>
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    1. POAttribute as dict of lists using middleman table with SQLAlchemy
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    1. USDenis Otkidach
    1. USDenis Otkidach
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    1. COUpdated my question with new code, can't get my own MyMappedCollection to work, any ideas?
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    2. COassociation_proxy is designed to work with standard collections only, but not multi-value dictionary. Subclassing MappedCollection is meaningless since no of its methods suite your needs. I'd avoid subclassing dict too as SQLAlchemy auto-magically wraps some dict's methods assuming value in dictionary is a mapped object. I've updated my answer with sample implementation which seems to work.
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      1. USDenis Otkidach
 

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