The reason I do this "whacky" scheme is a simple content management system. Take
this hirarchy for instance:
content
page
linklist
productlist
product
someproduct
So I can identify each content item by a unique id, and content is also type
tagged. Of course a linklist should reference pages in a many to many
relationship.
Actually I think once people get their head around ORM mapping techniques and OO
design you'll see a lot more of this pattern.
Quoting Michael Bayer <[EMAIL PROTECTED]>:
> the issue here is that your inheritance and your related table are
> both to the same table, i.e. 'foo'. the logic that is breaking is
> where it tries to determine "which property must be synchronized
> between parent and child object, or between parent, child, and
> association table", since honestly i never anticipated that the same
> table would be represented in two different but related mappers in
> quite that way.
>
> i am sure i'll come up with a patch for this one but i wonder if
> people will still be coming up with these wacky scenarios a year from
> now....
>
> On Feb 25, 2006, at 6:37 PM, Florian Boesch wrote:
>
> > I require that kind of thing, so I've assembled a little testcode
> > to demonstrate
> > the problems.
> >
> > Below is the vanilla many to many thing that doesn't error upon
> > defintion (with
> > one minor glitch at the mapper, see #comments)
> >
> > from sqlalchemy import *
> > from sqlalchemy.ext.proxy import ProxyEngine
> > engine = ProxyEngine()
> >
> > foo = Table('foo', engine,
> > Column('id', Integer, primary_key=True))
> >
> > bar = Table('bar', engine,
> > Column('id', Integer, primary_key=True))
> >
> > foo_bar = Table('foo_bar', engine,
> > Column('foo_id', Integer, ForeignKey('foo.id')),
> > Column('bar_id', Integer, ForeignKey('bar.id')))
> >
> > class Foo(object): pass
> > Foo.mapper = mapper(Foo, foo)
> > class Bar(object): pass
> > Bar.mapper = mapper(Bar, bar)
> >
> > # Bar.mapper.add_property('foos', relation(Foo, foo_bar))
> > # ==> sqlalchemy.exceptions.ArgumentError: relation(class, table,
> > **kwargs) is
> > # deprecated. Please use relation(class, **kwargs) or relation
> > (mapper,
> > **kwargs).
> >
> > Bar.mapper.add_property('foos', relation(Foo.mapper, foo_bar))
> >
> >
> > Now when I throw in inheritance as in
> >
> > bar = Table('bar', engine,
> > Column('id', Integer, ForeignKey('foo.id'), primary_key=True))
> > Bar.mapper = mapper(Bar, bar, inherits=Foo.mapper)
> >
> > and then try to
> > Bar.mapper.add_property('foos', relation(Foo.mapper, foo_bar))
> >
> > I get:
> > Traceback (most recent call last):
> > File "testalchemy.py", line 23, in ?
> > Bar.mapper.add_property('foos', relation(Foo.mapper, foo_bar))
> > File
> > "/usr/local/lib/python2.4/site-packages/SQLAlchemy-0.1.2-py2.4.egg/
> > sqlalchemy/mapping/mapper.py",
> > line 195, in add_property
> > prop.init(key, self)
> > File
> > "/usr/local/lib/python2.4/site-packages/SQLAlchemy-0.1.2-py2.4.egg/
> > sqlalchemy/mapping/mapper.py",
> > line 777, in init
> > self.do_init(key, parent)
> > File
> > "/usr/local/lib/python2.4/site-packages/SQLAlchemy-0.1.2-py2.4.egg/
> > sqlalchemy/mapping/properties.py",
> > line 191, in do_init
> > self._compile_synchronizers()
> > File
> > "/usr/local/lib/python2.4/site-packages/SQLAlchemy-0.1.2-py2.4.egg/
> > sqlalchemy/mapping/properties.py",
> > line 583, in _compile_synchronizers
> > self.primaryjoin.accept_visitor(processor)
> > File
> > "/usr/local/lib/python2.4/site-packages/SQLAlchemy-0.1.2-py2.4.egg/
> > sqlalchemy/sql.py",
> > line 749, in accept_visitor
> > c.accept_visitor(visitor)
> > File
> > "/usr/local/lib/python2.4/site-packages/SQLAlchemy-0.1.2-py2.4.egg/
> > sqlalchemy/sql.py",
> > line 819, in accept_visitor
> > visitor.visit_binary(self)
> > File
> > "/usr/local/lib/python2.4/site-packages/SQLAlchemy-0.1.2-py2.4.egg/
> > sqlalchemy/mapping/properties.py",
> > line 969, in visit_binary
> > self.func(binary)
> > File
> > "/usr/local/lib/python2.4/site-packages/SQLAlchemy-0.1.2-py2.4.egg/
> > sqlalchemy/mapping/properties.py",
> > line 575, in compile
> > raise AssertionError("assert failed")
> > sqlalchemy.exceptions.AssertionError: assert failed
> >
> > (a sidenote, assert failed isn't a very clever assert line :D)
> >
> > ----- End forwarded message -----
> >
> >
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