Iterating over related objects in Django: loop over query set or use one-liner select_related (or prefetch_related)

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I have a newsletter application where a newsletter has multiple articles within each issue. I want to display a summary page online that lists the newsletter year, volume and label, and then in an unordered list display all the articles in the issue. I am quite new to Django so I am trying to determine the best way to do this.

I have the models defined (just the relevant parts):

Models.py:

class Newsletter(models.Model):
    volume = models.ForeignKey(Volume)
    year   = models.IntegerField()
    season = models.CharField(max_length=6, choices=VOLUME_SEASON)
    label  = models.CharField(max_length=20)
    number = models.IntegerField()

class Article(models.Model):
    newsletter = models.ForeignKey(Newsletter)
    section    = models.ForeignKey(Section)
    title      = models.CharField(max_length=200)

What I want to see on the web looks like:

<h2>Spring 2012</h2>
<p>Volume 14, Number 1</p>
<ul>
    <li>Foo</li>
    <li>Bar</li>
    <li>Baz</li>
</ul>

<h2>Winter 2011</h2>
<p>Volume 13, Number 4</p>
<ul>
  <li>Boffo</li>
</ul>

Pretty simple. However, I am confused by the best way to write my view. Whether to use:

  • Two lists which I zip() and then iterate over in the template
  • Use the select_related() queryset
  • Use the prefetch_related() queryset

I have it working using the first option:

Views.py:

from django.shortcuts import render_to_response, get_object_or_404
from www.apps.newsletter.models import Newsletter, Article

def index(request):
    article_group = []
    newsletter = Newsletter.objects.all().order_by('-year', '-number')
    for n in newsletter:
        article_group.append(n.article_set.all())
    articles_per_newsletter = zip(newsletter, article_group)

    return render_to_response('newsletter/newsletter_list.html',
                              {'newsletter_list': articles_per_newsletter})

And then render it using the following template:

Newsletter_list.html:

{% block content %}
  {% for newsletter, articles in newsletter_list %}
    <h2>{{ newsletter.label }}</h2>
    <p>Volume {{ newsletter.volume }}, Number {{ newsletter.number }}</p>
    <p>{{ newsletter.article }}</p>
    <ul>
    {% for a in articles %}
      <li>{{ a.title }}</li>
    {% endfor %}
    </ul>
  {% endfor %}
{% endblock %}

Pretty straightforward, but as I am pretty new to Django I was wondering if what I am doing is completely inefficient in terms of its powerful ORM. I would love to not have to make a list on-the-fly and then zip() the two lists together if there is a faster way.

TIA.

1 Answers
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