[Zope3-dev] zwiki: performance of findChildren()

[Roché Compaan]

* Jeremy Hylton <jeremy@zope.com> [2003-04-25 19:50]:
> I'd like to understand it better too.  I think the idea is to represent
> relations between two objects using a BTree index with properties on the
> object themselves to keep a natural Python API.  Here's an example I've
> invented to have something concrete to talk about.
> 
> class SoftwareProject(Persistent):
> 
>     def __init__(self, name):
>         self.name = name
>         self.developers = rel
> 
> class Developer(Persistent):
> 
>     def __init__(self):
>         self.name = name
>         self.projects = rel
> 
> rel = relation(Developers, SoftwareProject)
> 
> zope3 = SoftwareProject("Zope3")
> jim = Developer("Jim Fulton")
> stevea = Developer("Steve Alexander")
> 
> zope.developers.add(jim)
> zope.developers.add(stevea)
> assert zope in stevea.projects
> 
> One idea is that if the relation is populated in one direction, it is
> also manifest in the other direction.  I think this means that the
> system is reponsible for providing referential integrity.
> 

I think the cardinality of the relationship is important too. If it is
a many to many relationship like the above then one would know that
zope3.developers and stevea.projects would both return sequences. But if
I register the relationship between SoftwareProject and Developer as a
many to one relationship:

    rel = relation(SoftwareProject, Developer, OneToMany)

then the following will hold true:

    assert zope3.developer.Name == 'Steve Alexander'

as well as:

    assert zope3 in steva.projects

-- 
Roché Compaan
Upfront Systems                 http://www.upfrontsystems.co.za