Question

I am creating little blog app. I want to return post, and (my problem), previous and next posts, so I can display them together with post. My current decision is very bad, because not only I load all Post objects, but also convert QuerySet to list. Here is a snippet from views.py:

def post(request, url):
        try:
            post = Post.objects.get(slug = url)
        except Post.DoesNotExist:
            raise Http404()
        posts = Post.objects.all().order_by('-date')
        index = list(posts).index(post)
        if index > 0:
            ppost = posts[index - 1] #previuos post
        else:
            ppost = None
        if index < len(posts):
            npost = posts[index + 1] #next post
        else:
            npost = None
        if not post.visible:
            raise Http404()
        return render_to_response('post.html',
                                  {'post': post, 'ppost': ppost, 'npost': npost},
                                  context_instance=RequestContext(request))

And here is models.py:

class Post(models.Model):
    slug = models.SlugField(unique=True)
    subject = models.CharField(max_length=150)
    abstract = models.CharField(max_length=300)
    content = models.TextField()
    author = models.ForeignKey(User)
    date = models.DateTimeField(auto_now_add=True)
    visible = models.BooleanField(default=False)
    tags = models.ManyToManyField(Tag, blank = True, null = True)

    def save(self, *args, **kwargs):
        self.abstract = self.content[:297] + "..."
        self.slug = slugify(self.subject)
        super(Post, self).save(*args, **kwargs)

    def __unicode__(self):
        return self.subject

    class Meta:
        ordering = ['-date']

I would appreciate any architectural ideas, how to implement this case. Any ideas actually :). Thank you in advance

Answer 1

You don’t have to implement fetching the next and previous instances yourself, it’s already builtin: http://docs.djangoproject.com/en/1.3/ref/models/instances/#django.db.models.Model.get_previous_by_FOO

If you want to tweak this a bit, for example to get the neighboring instances for non-date fields, see this thread on django users

With these model methods you can create a pager in your template like this:

<div id="pager">
    {% if object.get_prev_by_title  %}
        <a class="prev" href="{{ object.get_prev_by_title.get_absolute_url }}">
{{ object.get_prev_by_title }}</a>
    {% endif %}
    {% if object.get_next_by_title  %}
        <a class="next" href="{{ object.get_next_by_title.get_absolute_url }}">
{{ object.get_next_by_title }}</a>
    {% endif %}
</div>