Django one to many relationship: number of objects

Question

here is my models:

class Story(models.Model):
    writer = models.ForeignKey(UserProfile, blank=False, null=True)
    .
    .
    .

class Comment(models.Model):
    on_story = models.ForeignKey(Story, related_name="comments", blank=False, null=False)
    .
    .
    .

How do I get the number of comments related to a specific Story, and inject that into a view?

Answer 1

If you need the comment count for multiple stories, I would strongly recommend to use annotations instead of calling comments.count() on each story:

from django.db.models import Count

stories = Story.objects.order_by("-date_published").annotate(comment_count=Count('comments'))

This will reduce the number of queries from N+1 to just 1, doing the COUNT in the database using joins, instead of a separate query for each count. The count is then accessible as follows:

{% for story in stories %}
    {{ story.comment_count }}
{% endfor %}

Answer 2

You can use QuerySet.count through comments attribute (related_name).

Use the following in the view function:

comment_count = specific_story.comments.count()
# do something with `comment_count`

UPDATE Use .comments.count in template:

{% for story in stories %}
    ... {{ story.comments.count }} ...
{% endfor %}