[Sqlalchemy-tickets] Issue #3189: Combining association proxy and ordering list does not work (zzzeek/sqlalchemy)

[Wichert A. <iss...@bi...>]

New issue 3189: Combining association proxy and ordering list does not work
https://bitbucket.org/zzzeek/sqlalchemy/issue/3189/combining-association-proxy-and-ordering

Wichert Akkerman:

I want to create an ordered many-to-many relationship, where I only really care about the order from one side of the relationship. I tried to model that by creating a relationship using `ordering_list`, and adding an `association_proxy` on top of that. That works fine when adding items to the list, but fails when trying to remove items from the list.

I have attached a small python script that reproduces the error. This is the essential part of it:

```python
class FolderImage(BaseObject):
    __tablename__ = 'folder_image'

    image_id = schema.Column(types.Integer(),
        schema.ForeignKey('image.id'), primary_key=True)
    folder_id = schema.Column(types.Integer(),
        schema.ForeignKey('folder.id'), primary_key=True)
    position = schema.Column(types.Integer())

    def __init__(self, image=None, **kw):
        BaseObject.__init__(self, image_id=image.id, **kw)


class Image(BaseObject):
    __tablename__ = 'image'
    id = schema.Column(types.Integer(), primary_key=True, autoincrement=True)


class Folder(BaseObject):
    __tablename__ = 'folder'

    id = schema.Column(types.Integer(), primary_key=True, autoincrement=True)
    _images = orm.relationship('FolderImage', order_by=[FolderImage.position],
        collection_class=ordering_list('position'))
    images = association_proxy('_images', 'image')

img = Image()
folder = Folder(images=[img])
session.add(folder)
session.flush()
folder.images = [img]
session.flush()
```

Running this results in:

```
sqlalchemy.exc.IntegrityError: (IntegrityError) NOT NULL constraint failed: folder_image.image_id u'INSERT INTO folder_image (folder_id, position) VALUES (?, ?)' (1, 0)
```


I am wondering if this is a regression since I apparently managed to do this a couple of years ago (see [this post](https://groups.google.com/forum/#!topic/sqlalchemy/S4_8PeRBNJw).