Re: Using Aggregate and Count

On Wednesday, 20 November 2013 19:11:26 UTC, Timothy W. Cook wrote:

I see there was a similar question on this issue earlier today but
alas it didn't answer my question.

In my app I have models for:
Project:  a project (not really part of this question but used for
context in the question).
Paper: an academic paper description
Review: a review of a paper
... other things not pertinent.

I can list Projects and from there I can list Papers assigned to each project.
In the listing of papers I want to show how many reviews there are for
each Paper.

Paper has a ForeignKey to Project and Review has a ForeignKey to Paper.

I have this code as my view:

class PapersListView(ListView):
    model = Paper
    template_name = 'papers/papers_list.html'

    def get_context_data(self, **kwargs):
        context = super(PapersListView, self).get_context_data(**kwargs)
        papers = Paper.objects.filter(project__id=self.kwargs['pk'])
        review_count = Review.objects.aggregate(review_count=Count('paper'))
        print(review_count)
        context['papers'] = papers
        context['review_count'] = review_count
        return context

and this in my template:

               <div class="table">
                    <table class="listing" cellpadding="2" cellspacing="2">
                        <tr>
                            <th>Title</th>
                            <th>Reviews</th>
                            <th>Year</th>
                            <th>Journal</th>
                            <th>Current Stage</th>
                        </tr>
                        {% for p in papers %}
                        <tr>
                            <td class="style1"><a href="#">{{p.title}}</a></td>
                            <td>{{p.review_count}}</td>
                            <td>{{p.year_published}}</td>
                            <td>{{p.journal}}</td>
                            <td>{{p.current_stage}}</td>
                        </tr>
                       {% endfor %}
                    </table>
                </div>

The print() inserted in the view gives me this:
{'review_count': 2}

In the rendered template the Reviews column is empty.

There are two Review instances in the database.  But, they are for two
separate Papers in two separate Projects.  So, my guess is that I have
two problems but after scouring the docs I can't determine where the
mistakes/misunderstandings are.

Any help is appreciated.

Cheers,
Tim

You're accessing a `review_count` attribute via each Paper instance, but you haven't set up anything that would do that - you only have a single top-level `review_count` dictionary.

Instead of a separate `aggregate` call, you should be using `annotate` on the original Paper queryset:

    papers = Paper.objects.filter(project__id=self.kwargs['pk']).annotate(review_count=Count('review'))

Now each element in `papers` has a `review_count` attribute.

-- 

DR.

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