[Zope-dev] Specialists and __bobo_traverse__

[Steve Alexander]

Roch'e Compaan wrote:

> Recent sightings of the use of __bobo_traverse__ in SkinScript gave me hope
> of giving users a more useable breadcrumbs trail in the case where I have
> nested specialists.
> 
> My TaskTemplates specialist is nested inside my RequestTypes specialist.
> When I retrieve a dataskin from the RequestTypes specialist I have a tab
> that lists TaskTemplates for that RequestType specialist.  Following a link
> from the TaskTemplate list takes you to that instance.
> 
> Thus results in a url like this:
> 	/RequestTypes/<request type instance>/Task Templates/<task template
> instance>,
> and what I ideally want is:
> 	/RequestTypes/<request type instance>/<task template instance>.
> 
> I read all the comments about __bobo_traverse__ and created a python method,
> "traversal_method" inside the "RequestTypes" specialists.  I must admit that
> I don't really understand Zope's traversal machinery yet and would
> appreciate some guidance.

With your code below, and with a concrete example, can you say what you 
want to happen, and what actually does happen?

> My SkinScript for RequestTypes:
> 
> WITH SELF COMPUTE __bobo_traverse_=traversal_method

You'll want another underscore in there: __bobo_traverse__

> My traversal_method:
> 
> ob = getattr(self, name)
> if ob is not None:
 >   return ob

If ob is not found, you'll get an error raised. You need to have some 
sort of marker for the default value.

marker=[]
ob=getattr(self, name, marker)
if ob is not marker:
   return ob
# continue your method

Of course, you only need one marker in your class. You can do that if 
you implement your method as an external method, or perhaps with a 
default value for an argument on you python method.

Or, you could not worry about creating a new empty list on each request.

--
Steve Alexander
Software Engineer
Cat-Box limited
http://www.cat-box.net