Hi guys,
I've got models like this:
class Category(model.Model):
pass
class City(model.Model):
pass
class Listing(model.Model):
city = model.ForeignKey(City)
categories = model.ManyToMany(Category, related_name='listings')
and I have a template that iterates over all the categories and all the
listings for each category for a given city, e.g.,
ALL LISTINGS IN CITY=NEW YORK
Bars : Category
...
Restaurants : Category
Restaurant1 : Listing
Restaurant2 : Listing
A simple view preparation of the data would be:
city='new york'
for category in Category.objects.all():
for listing in category.listings.filter(city=city):
# listing here
But I cannot do this in a template since templates don't allow
arguments to methods in the for loop, e.g., I cannot do
{% for listing in category.listings.filter(city=city) %}
So, I can prepare the viewdata in a context object and pass that to the
template. The most obvious choices all aren't very pretty:
# alternative 1: put the objects into the context,
# put the listings in the objects
context['categories'] = Categories.objects.all()
for category in context['categories']:
category.city_listings = category.listings.filter(city=city)
# alternative 2: put the objects into the context,
# put the listings in a separate place
context['categories'] = Categories.objects.all()
for category in context['categories']:
context[category.name + '_city_listings'] \
= category.listings.filter(city=city)
# alternative 3: create new structures for all data
context['categories'] = []
for category in Category.objects.all():
c = category.__dict__.copy()
c['listings'] = category.listings.filter(city=city)
context['categories'].append(c)
These alternatives all have different problems:
[1] Dynamically adding an attribute to the objects doesn't seem nice;
is it?
[2] In the template, given the category object, how can I access the
city listings?
[3] Cumbersome, and isn't copying the object's dict like this a bit
dangerous and wasteful?
A final alternative is to create a templatetag for this, but this also
seems a bit cumbersome.
What is the recommended way in these cases?
Rgds,
Bjorn
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