Aggregate related integer-field values in Django template

Question

I have this model which is related to a Node model,

class Views(models.Model):
    related_tree = models.ForeignKey(Node, on_delete=models.CASCADE, blank=True, null=True, related_name='related_views')
    views_count = models.PositiveIntegerField(null=True, blank=True, default=0)
    user = models.ForeignKey(CustomUser, on_delete=models.CASCADE, blank=True, null=True)

    def __str__(self):
        return self.related_tree.name

In the template when i query a list of the Node's objects i want to aggregate the value of the 'views_count' of each object.

I have tried this in my template

{% for tree in tree_result|slice:":14" %}
{% for view in tree.related_views.all %}

{{ view.views_count }}
{% endfor %}
{% endfor %}

i have all the related count_view of the current tree but what i want to do is to aggregate the value of the related field and show it within the for loop of tree_result.

Any suggestions please ?

EDIT :

def ResultSearch(request, search):
    formatted_search = search.split('+$')
    filter = Q()
    cases = {}
    get_result_list = [x for x in search.split('+$') if x != '']
    for i, keyword in enumerate(get_result_list):
        filter |= Q(name__icontains=keyword)
        filter |= Q(Tags__icontains=keyword)
        cases['keyword_match_{}'.format(i)] = Case(
            When(name__icontains=keyword, then=1),
            default=Value(0),
            output_field=models.IntegerField(),
        )
    result = Node.objects.filter(
        filter,
        tree_type='root',
        published=True,
        tunisia_office=True
    ).annotate(
        **cases
    ).annotate(
        total_views=Sum('related_views__views_count'),
        num_bookmarks=Count('bookmarked_by'),
        keywords_matched=reduce(add, (F(name) for name in cases))
    ).order_by('-keywords_matched', '-num_bookmarks')

    context = {
    'searched_keyword': formatted_search,
    'result_list': result,
    }

Willem Van Onsem · Accepted Answer · 2019-07-28T12:57:11.683

2

You should annotate your queryset in the view, like:

from django.db.models import Sum

Node.objects.annotate(
    total_views=Sum('related_views__views_count')
)

The Nodes that arise from this queryset will have an extra attribute .total_views which is the sum of the views_count of the related Views.

In your template you can then render this like:

{% for tree in tree_result|slice:":14" %}
    {{ tree.total_views }}
{% endfor %}

Note: please do not aggregate in the template. Templates are not designed to implement business logic. A template should only contain "render logic". By using annotations, you will let the database do the aggregations. Databases are usually optimized to perform such tasks.

edited Jul 28 '19 at 12:57

answered Jul 28 '19 at 12:49

Willem Van Onsem

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Thank you for your answer, the issue is that actually when i add {{ tree.total_views }} into the template every time i add a +1 into the view count i have in the template an increment of 4, for i.e actually i have 3 views and in the template is 16 – Farhani Walid Jul 28 '19 at 14:21
@FarhaniWalid: you can update this in the view as well, like `tree.related_views.update(views_count=F('views_count')+1)`. That being said, a property with side effects would probably not be the best code design. – Willem Van Onsem Jul 28 '19 at 14:24
db side everything seems to be ok, the increment of +1 is working but in the telmplate rendered i have an increment of 4, i have added the entire view, maybe the issue is comin from there ? – Farhani Walid Jul 28 '19 at 14:27
I will accept your answer and i will post anew one for the new issue that i am facing, thank you anyway – Farhani Walid Jul 28 '19 at 14:49

Aggregate related integer-field values in Django template

1 Answers1