Re: [Sqlalchemy-users] Many to Many mapping and inheritance

[Michael Bayer]

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)

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