On Sat, Jul 11, 2009, Daniel Roseman <dan...@roseman.org.uk> wrote:
>> I think this means that I need to add a routine to my admin.py so that
>> when the user hits Save, it will also manually assemble the information
>> and save it for the affected models.
>>
>> Is that correct? If so, what is doing this called, so I can look it up
>> in the documentation?
>Well, this is called a Signal, and you wouldn't do it in admin.py
>necessarily - you would connect a function to the post-save signal so
>that any time the user is saved, the group information is also
>collected and saved.
>
>However I think a better solution for you would be to investigate
>django-mptt. MPTT is an algorithm that allows you to efficiently
>retrieve hierarchical data, so that in your example you would be able
>to get the user's group and all of its parent groups in a single query
>rather than having to denormalise the data and store it per user.
I already use MPTT to manage the hierarchy, and in fact my functions use
MPTT's get_ancestors().
But it's complicated - because a person can be a member of more than one
entity, and because a person also has a home_entity, in order to get a
clean list (no duplicates) of the entities they belong to I have a
function called gather_entities():
def gather_entities(self):
entitylist = [self.home_entity]
entitylist.extend(self.home_entity.get_ancestors())
for entity in self.entities.all():
entitylist.append(entity)
entitylist.extend(entity.get_ancestors())
entitylist.sort()
last = entitylist[-1]
for i in range(len(entitylist)-2, -1, -1):
if last==entitylist[i]: del entitylist[i]
else: last=entitylist[i]
return entitylist
That's not too bad, but to go the opposite way, and to find a list of
members from a given entity will require a lot of poking around, it
seems to me.
Daniele
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