django select_related in template

Question

Sometimes it makes sense to use select_related in a django template. For example, say I have a class extending DetailView

class DemoCarView(DetailView):
    model = Car

Based on the following contrived model

# Cars
class Car(models.Model):
    name = models.CharField(max_length=32)

# Manufacturers
class Manufacturer(models.Model):
    name = models.CharField(max_length=32)

# Parts
class Part(models.Model):
    name = models.CharField(max_length=32)
    car = models.ForeignKey(Car)
    manufacturer = models.ForeignKey(Manufacturer)

The html template is then

{{ car.name }}
<ul>
{% for part in car.part_set.all %}
    <li>{{ part.name }} - {{ part.manufacturer.name }} </li>
{% endfor %}
</ul>

This works perfectly to get the car, the parts that comprise it, and the manufacturers of those parts. However, this will use 2+number_of_parts SQL queries to do so. Easily fixed like so:

{{ car.name }}
<ul>
{% for part in car.part_set.select_related.all %}
    <li>{{ part.name }} - {{ part.manufacturer.name }} </li>
{% endfor %}
</ul>

Now the optimum of 2 queries is run. However, select_related is joining the Parts with every Foreign Key that it has. Is there a way to restrict this to just the desired related tables. In Python it's just:

Part.objects.select_related('manufacturer').filter(car=car)

Can this be done in the template?

Note: I know I can do this in the view very easily by returning a context for 'car' and one for 'parts' with select_related('manufacturer') on the filter, but it's quite a bit more code compared to the DetailView sub-class I've used above. Something like this:

class DemoCarViewPreload(TemplateView):
    template_name = 'demo/car_detail_preload.html'
    def get_context_data(self, **kwargs):
        context = super(DemoCarViewPreload, self).get_context_data(**kwargs)
        car = Car.objects.get(pk=kwargs.get('pk'))
        context['car'] = car
        context['parts'] = Part.objects.select_related('manufacturer').filter(car=car)
        return context

However, this requires the template to be more specific to this view as it will now need to use the 'parts' context rather than car.part_set.all. Also, it's simply more work to make this view in the first place.

Answer 1

How about a simple method on the Car model?

class Car(models.Model):
    ...
    def parts_with_manufacturers(self):
        return self.part_set.select_related('manufacturer')

and then

{% for part in car.parts_with_manufacturers %}
    <li>{{ part.name }} - {{ part.manufacturer.name }} </li>
{% endfor %}