Develop Reference

How do I get reverse reference in Django template?

Apologies if the title doesn't make much sense. I don't quite understand what I lack in knowledge.
I have a Post and Comment models in my Django project. What I'm trying to do is list out all the Blog posts, and show NUMBER OF COMMENTS OF EACH POST. Please see my codes below.
models.py
class Blog(models.Model):
objects = models.Manager()
title = models.CharField(max_length=100, blank=True)
body = models.CharField(max_length=10000, blank=True)
created_at = models.DateField(auto_now_add=False)
class Comment(models.Model):
objects = models.Manager()
post = models.ForeignKey(Blog, on_delete=models.CASCADE, related_name='comment')
views.py
def main_page(request):
all_blogs = Blog.objects.all()
context = {
'blog' : blog,
}
return render(request, 'main/home.html', context)
template
{% for b in blog %}
<div>
<p>{{b.title}}</p>
<div>
{{WHERE THE NUMBER OF THIS POST'S COMMENTS IS DISPLAYED}}
</div>
</div>
{% endfor %}
All I need is the number of the comments, but have no idea how to do it. Is there a way to make this possible in the template? Or do I have to add some codes in views.py?

You can annotate the Blog objects with the number of related Comments with:
from django.db.models import Count
def main_page(request):
all_blogs = Blog.objects.annotate(
num_comments=Count('comment')
)
context = {
'blogs' : blogs
}
return render(request, 'main/home.html', context)
The Blog objects that arise from that queryset will have an extra attribute .num_comments with the number of related comments:
{% for blog in blogs %}
<div>
<p>{{ blog.title }}</p>
<div>
{{ blog.num_comments }}
</div>
</div>
{% endfor %}

How do i query for comment in Django

I am new in Django and I have been following tutorials online. I am having problem on how to display the comments.
How do i query for comments in views, so i can display comments for a particular post.
Model:
class Post(models.Model):
poster_profile = models.ForeignKey(settings.AUTH_USER_MODEL,on_delete=models.CASCADE, blank=True,null=True)
image_caption = models.TextField(blank=True, null=True)
class Comments (models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL,on_delete=models.CASCADE, blank=True,null=True)
commented_image = models.ForeignKey(Post, on_delete=models.CASCADE, null=True, blank=True)
comment_post = models.TextField()
Views.py:
def home_view(request):
comment = Comments.objects.all() #This is getting all comment in all post, how do i query for comment in a particular post.
context{'comment':comment}
return render(...)
Template:
{% for com in comment %}
<p>{{ com.comment_post }}</p>
{% endfor %}

You can do
post = Post.objects.get(id=1)
comment = post.comments_set.all()
Following Relationships "Backward"
If a model has a ForeignKey, instances of the foreign-key model will have access to a Manager that returns all instances of the first model. By default, this Manager is named FOO_set, where FOO is the source model name, lowercased. This Manager returns QuerySets, which can be filtered and manipulated as described in the “Retrieving objects” section above.
Note this behaviour can be overridden.
You can override the FOO_set name by setting the related_name parameter in the ForeignKey definition. For example, if the Entry model was altered to blog = ForeignKey(Blog, on_delete=models.CASCADE, related_name='entries'), the above example code would look like this:
Edit #2:
views.py:
def home_view(request):
posts = Post.objects.all().reverse()[5]
context{ 'posts': posts, }
return render(...)
Now in your templates you can do something like:
{% if posts %}
{% for post in posts %}
{{ post.image_caption }}
{% for comment in post.comments_set.all %}
{{ comment.comment_post }}
{% endfor %}
{% endfor %}
{% endif %}

First of all, take a look at Django queryset documentation, especially select_related for this kind of issues (to reduce number of queries to database). I didn't try but following snippet must work.
class Post(models.Model):
poster_profile = models.ForeignKey(settings.AUTH_USER_MODEL,on_delete=models.CASCADE)
image_caption = models.TextField(blank=True, null=True)
class Comments (models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL,on_delete=models.CASCADE)
commented_image = models.ForeignKey(Post, related_nam="comments", on_delete=models.CASCADE)
comment_post = models.TextField()
...
def home_view(request):
post = Post.objects.filter(id=request.data.get('post_id')).select_related("comments") # specify the post anyhow ..
comments = post.comments
context{'comment': comments}
return render(...)

def home_view(request):
particular_Post= Post.objects.get(id=1)
comment = Comments.objects.get(Post=particular_Post)
context{'comment':comment}
return render(...)
to understund Query in django i suggest U to start by
python manage.py shell
and Import you're Models

What is wrong with my nested for Loop in a django Template?

I am trying to create a template with Django that loops through Posts and for each Post loops through all Pictures.
I already looked at some answers to other Questions but I can not find my error.
Models:
class Post(models.Model):
Post_Title = models.CharField(max_length=200)
Post_pub_date = models.DateField('date published')
Post_Author = models.CharField(max_length=100)
Post_Text = models.TextField()
def __str__(self):
return self.Post_Title
class Picture(models.Model):
Post = models.ForeignKey(Post, on_delete=models.CASCADE)
Picture = models.ImageField()
Picture_Name = models.CharField(max_length=100, null=True, blank=True)
def __str__(self):
return self.Picture_Name
Views:
class PostView(generic.ListView):
template_name = 'myblog/index.html'
context_object_name = 'Post_List'
def get_queryset(self):
"""
Returns Posts
"""
return Post.objects.order_by('-Post_pub_date')
Template:
{% for Post in Post_List %}
<h1 class="mb-4">{{Post.Post_Title}}</h1>
<span class="category">{{Post.Post_Author}}</span>
<span class="mr-2">{{Post.Post_pub_date}}</span>
<div class="post-content-body"><p>{{Post.Post_Text}}</p>
{% for Picture in Post.Picture_set.all %}
<div class="col-md-12 mb-4 element-animate">
<h2>{{Picture.Picture_Name}}</h2>
<img class="col-md-12 mb-4 element-animate" src="{{ MEDIA_URL }}{Picture.Picture}}">
</div>
{% endfor %}
</div>
{% endfor %}
The Post_Title, Post_Author, Post_pub_date and Post_Text are displayed fine. Just the nested For loop is not producing any Picture_Name or Picture as if the Picture_set.all is empty.
As mentioned above I tried to find my error in different Posts like this but could not find it.
Thanks for your help.

Following relationship backward, you need to write related model name from a small letter, even if model name starts from large letter:
{% for Picture in Post.picture_set.all %}
This is how it works in Django shell and i suppose in templates it is the same.

The issue isn't the nested for loop it's the view.It only returns a query for your Post, you don't pass any Photos to your template.

List of posts not displaying - django

I have created a post model and would like to view the posts in post_list. While creating the new post, it is redirecting to post_list but not displaying any post.
Also, in my post_form I have rendered the fields manually by using django templates. I couldnt figure out where I have made the mistake. Can someone please help me out. Thanks
models.py
class Post(models.Model):
author = models.ForeignKey(User, on_delete = models.CASCADE)
slug = models.SlugField(unique=True, blank=True, default=uuid.uuid1)

By default the context_object_name is object_list
Either you access your Posts list in template with object_list
{% for post in object_list %}
{{ post }} <!-- with lowercase -->
{% endfor %}
Or you change the context_object_name to post_list, so that way you will be able to access the post list with post_list in template
class PostListView(ListView):
model = Post
context_object_name = 'post_list'

You probably need to use lowercase variable name in your post_list.html.
For instance, {{ Post.title }} should probably be lowercase {{ post.title }}.
There are a few places to change that.

How to create a form field for every foreignkey in manytomany relationship in Django

I don't understand how to build a specific form in Django.
First of all here are my models:
class Category(models.Model):
name = models.CharField(max_length=200, unique=True)
class Assessment(models.Model):
name = models.CharField(max_length=200)
pub_date = models.DateTimeField(verbose_name=_('date published'), default=timezone.now)
classgroup = models.ForeignKey(ClassGroup, verbose_name=_('class'), on_delete=models.CASCADE, related_name='+')
category = models.ManyToManyField(Category, through='AssessmentScale', through_fields=('assessment', 'category'),)
total = models.IntegerField()
class AssessmentScale(models.Model):
assessment = models.ForeignKey(Assessment, on_delete=models.CASCADE)
category = models.ForeignKey(Category, on_delete=models.CASCADE)
value = models.IntegerField()
I would like to have a form like this html form. Actually, an assessment scale is sub-divided into different categories. So when I create an assessment, I'd like have a form field for each category allowing to add a value via my custom intermediary model AssessmentScale. But I really don't know the Django way to build this form. I read this post, which is similar I think, and someone advised the use of Inline model formsets. But I don't understand how to solve my problem with the latter. Could you help me?

I had no answer from Stackoverflow but a friend of mine solved my problem like this with inline formset:
# forms.py
class AssessmentForm(ModelForm):
class Meta:
model = Assessment
exclude = ('category',)
CategoryAssessmentFormSet = inlineformset_factory(
Assessment,
Assessment.category.through,
fields=['category', 'value'],
can_delete=False,
extra=Category.objects.count(),
max_num=Category.objects.count(),
widgets={'category': Select(attrs={'hidden': 'true'})}
)
in my view, to render the formset:
# views.py
initial = [{'category': category} for category in Category.objects.all()]
formset = CategoryAssessmentFormSet(initial=initial)
Select is hidden but I still want the name of the selected field, in my template:
# template
{{ formset.management_form }}
{% for form in formset %}
<div class="p-2">
{% for value,selected in form.fields.category.choices %}
{% if value == form.category.value %}{{ selected }}{% endif %}
{% endfor %}
{{ form.category }}
</div>
<div>
{{ form.value}}
</div>
{% endfor %}