Django - usage of prefetch_related - django

Question

no matter how many tutorials/documentation i read i still don't quite understand how exactly i'm supposed to be using prefetch_related.
My models.py:
class ProfileComment(models.Model):
author = models.ForeignKey('Profile', on_delete=models.CASCADE, null=True)
date_posted = models.DateTimeField(default=timezone.now, editable=False)
body = models.CharField(max_length=180, blank=True)
...
class Profile(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE, related_name='profile')
comments = models.ManyToManyField(ProfileComment, related_name='comments', blank=True)
avatar = models.FileField(upload_to=avatar_folder, default='user-avatar/default.png')
...
My views.py:
profile = Profile.objects.prefetch_related('comments').get(user=request.user)
And in template:
{% for comment in profile.comments.all %}
<div>
<p>Author: {{ comment.author.user }}</p><img src="{{ comment.author.avatar.url }}">
<p>Message: {{ comment.body }}</p>
<p>Date posted: {{ comment.date_posted }}</p>
</div>
{% endfor %}
However, no matter what i put in prefetch_related, amount of queries just go up by like 5 for every record

Answer 1

.prefetch_related(…) [Django-doc] should be used to fetch related objects for a queryset in bulk. Since you write:
….get(user=request.user)
however it will not make any difference, since you only retrieve a single object, and it will thus prefetch the comments in an extra query.
What you can minimize however is the number of extra queries that originate from comment.author.user. This will make two extra queries per comment, since ForeignKeys are loaded lazily.
Your view can thus look like:
profile = Profile.objects.get(user=request.user)
comments = profile.comments.select_related('author', 'author__user')
where you pass both profile and comments to the template, and then retrieve it with:
{% for comment in comments %}
<div>
<p>Author: {{ comment.author.user }}</p><img src="{{ comment.author.avatar.url }}">
<p>Message: {{ comment.body }}</p>
<p>Date posted: {{ comment.date_posted }}</p>
</div>
{% endfor %}
here we thus read the comments from a queryset where we fetch the profile and the user of that profile in the same query. As a result we will make two queries: one for the Profile, and one for all the Comments including the .author and .author.user.