Hi list
This message is about using pyramid, rather than about its development. I hope
that's okay.
I'm new to the traversal mechanism for managing resources and views. I really
like the idea of a resource tree. I thought I'd write a quick note on how I'm
using it in the hope of drawing comments and comparisons. Particularly, I'll
describe what I've done to make any instance of a tree resource location-aware,
even if it wasn't reached by traversal.
Using traversal with a resource tree that looks like /foo-1/bar-2/baz-3 I find
it very convenient to build URLs using the request.resource_url interface. I
often want to build lists of URLs like this:
for baz in bar_instance.bazzes:
request.resource_url(baz)
I don't want to say request.resource_url(bar_instance, 'baz-%s' % baz.id)
because I don't want to spread around responsibility for representing the
resource tree and because, in the real case, the required call to resource_url
would be even uglier.
For all of my tree resources there is a natural parent (and it makes sense to
assume that if they exist then they can be located on the resource graph; I
never have to deal with resources that are disconnected in principle) so I can
say, for example
class Baz:
@property
def __name__(self):
return 'baz-%s' % self.id
@property
def __parent__(self):
return self.bar
which neatly enforces the structure of the resource graph in general. The
trouble is with the first layer of children in the tree. They need to point at
the application root.
If I have an instance of one of these first layer children that wasn't loaded
by traversal, then the only way I can think of to get at the application root
directly is via pyramid.threadlocal.get_current_request. That would make my
domain models dependent on pyramid which doesn't seem very natural.
Conceptually, I suppose the resources should sort out their own tree root
anyway, rather than trying to look somewhere else for it. And so my resource
package grew two new functions, set_tree_root and get_tree_root.
The application root factory contains
class AppRoot:
def __init__(self, request):
set_tree_root(self)
and top-level resources contain
class Foo:
@property
def __parent__(self):
return get_tree_root()
Behind the scenes, those two functions modify and access a thread-local
variable.
Does this sound broadly reasonable? Am I going to run into problems later? How
do you usually implement and use the resource tree?
Regards
Norman
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