Re: [SQLObject] Feature Request: Can Registry call a factory method if a class is not found?

[Ian B. <ia...@co...>]

Scott Sanders wrote:
>> I'm not entirely clear what you are thinking.  Right now the registry 
>> tracks classes, but it never returns classes.  Instead class 
>> references are pushed into the places they are needed, using callbacks 
>> which are triggered on class creation.  So I'm not sure where this 
>> would fit.
> 
> 
> The registry always returns a class when asked (for classes in joins, 
> etc),  or am I just smoking something???  I understand it never 
> generates a class.

The registry is meant to deal with circular references, which is why it 
doesn't return classes at all.  Since if A depends on B, and B depends 
on A, the calls will look like:

class A:
     my_b = registry.getClass('B') # registry goes off and creates B...

class B:
     my_a = registry.getClass('A') # but A doesn't exist yet, and
     # it won't until B is finished being created


Instead it works like:

import classregistry
registry = classregistry.registry('default')

class A:
     pass
registry.addClassCallback('B', lambda cls: A.my_b = cls)
registry.addClass(A)
# So far the registry hasn't done anything at all

class B:
     pass
registry.addClassCallback('A', lambda cls: B.my_a = cls)
# The registry immediately calls that lambda passing in A
registry.addClass(B)
# The registry now calls the previous lambda, passing in B


Maybe it would be helpful if the registry had a method to return the 
names of all the classes that are still pending?  That would be:

def pendingClasses(self):
     return self.callbacks.keys()

After you've loaded a class, you could check if there were any pending 
classes, and try to load them up.

-- 
Ian Bicking  /  ia...@co...  /  http://blog.ianbicking.org