Combining association proxy and ordering list does not work

[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:

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.

[Mike Bayer]

I've got nothing on ordering list. it's subject to subtle issues quite often that are hard to diagnose. do you have any insight on a potential patch ?

[Mike Bayer]

this has nothing to do with ordering list, take it out of the example and nothing changes...the use of assocation proxy is just wrong, plus you need a cascade delete, etc., works fine:

import sqlalchemy
from sqlalchemy import orm
from sqlalchemy import schema
from sqlalchemy import types
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.associationproxy import association_proxy
from sqlalchemy.ext.orderinglist import ordering_list


metadata = schema.MetaData()
BaseObject = declarative_base(metadata=metadata)


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())

    image = orm.relationship("Image")
    folder = orm.relationship("Folder", back_populates='_images')


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],
        back_populates='folder',
        cascade='all, delete-orphan',
        collection_class=ordering_list('position')
        )
    images = association_proxy(
        '_images', 'image', creator=lambda img: FolderImage(image=img))


engine = sqlalchemy.create_engine('sqlite:///:memory:')
metadata.create_all(engine)
sm = orm.sessionmaker(bind=engine)

session = orm.scoped_session(sm)

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

[Mike Bayer]

reopen if you have an updated example that shows something...