one hunch is that the B.get() method wants to receive a_id and b_id
as the arguments, i.e. B.get(1,1). the primary key of an inherited
mapper, across 'tablea' and 'tableb', is determined by:
x = join(tablea, tableb)
(x.onclause is now tablea.a_id==tableb.b_id)
the mappers primary_key cols, which are used in a get() ==
x.primary_key
the join will determine the primary key via: left.primary_key +
right.primary_key
which is: [a.a_id, b.b_id]
yup, i bet thats just it then.
So. what kind of rule to make this more intuitive? how about this:
[c for c in left.primary_key if not c.foreign_key.references(right)]
+ [c for c in right.primary_key if not c.foreign_key.references(left)]
?
On Mar 3, 2006, at 3:55 PM, Jeff Watkins wrote:
Now that I've got the ActiveMapper code working to my satisfaction,
I'm trying to add inheritance. This is proving to be no small task.
At the moment, I'm modelling things as follows:
class A(ActiveMapper):
class mapping:
a_id= column( Integer, primary_key=True )
a_field= column( Unicode(40) )
class B(A):
class mapping:
b_id= column( Integer, foreign_key="a.a_id", primary_key=True )
b_field= column( Unicode(40) )
(Note: these are totally fictitious classes. I'm actually working
on an Identity provider for TurboGears.)
In the __init__ method for the ActiveMapperMeta class, I check to
determine whether the class inherits from another class with a
mapper and if so, the new mapper is created using the inherits
keyword argument. This seems to work just fine when I'm creating
new objects, however, retrieving those objects seems problematic.
Let's say I want to retrieve a B; I use the following code:
b= B.get(1)
Instead of my glorious B, I get:
Traceback (most recent call last):
File "<console>", line 1, in ?
File "/Users/jeff/Projects/Web/sqlalchemy/lib/sqlalchemy/mapping/
mapper.py", line 272, in get
return self._get(key, ident)
File "/Users/jeff/Projects/Web/sqlalchemy/lib/sqlalchemy/mapping/
mapper.py", line 286, in _get
params["pk_"+primary_key.key] = ident[i]
IndexError: tuple index out of range
So I ask, "what gives?" Everything works fine if I execute:
b= B.select()[0]
But that's not very helpful.
--
Jeff Watkins
http://newburyportion.com/
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