Django many to one relationship

Question

Suppose I have a model like this :

from django.db import models
from ckeditor.fields import RichTextField
from taggit.managers import TaggableManager


class Post(models.Model):
    title = models.CharField(max_length=50)
    pub_date = models.DateTimeField(auto_now_add=True)
    content = RichTextField()
    tags = TaggableManager()

    def __unicode__(self):
       return self.title


class Comments(models.Model):
      post_id = models.ForeignKey(Post)
      author = models.CharField(max_length=50)
      content = models.TextField()
      publish_date = models.DateTimeField(auto_now_add=True)

     def __unicode__(self):
        return self.content

Now for example i have many comments for a blog post id 1, then how would retrieve all the comments in that particular post ?

Answer 1

First of all you should rename your Comments model to Comment, as it represent a single comment. Then you would do this:

post = Post.objects.get(pk=1)
comments = post.comment_set.all()

You can read more about reverse relationships in the documentation.

Edit: Yes, you can also do this in a template. Provided you get a post object in a variable named post you could do something similar to this (obviously you would need to add some HTML):

{% for comment in post.comment_set.all %}
    {{ comment.author }}: {{ comment.content }}
{% endfor %}

Answer 2

When you have a relation like that, you can access related objects through the objects managers generated by Django.

For accessing all the comments from a post you can:

comments = one_post.comment_set.all()

you can change the manager´s name (comment_set) by specifying the related_name option in the ForeignKey field

post_id = Foreignkey(Post, related_name=comments)

and the you can:

comments = one_post.comments.all()

See: ForeignKey reference of Django documentation.

Answering to you last question:

You could write a template for listing the comments like this:

<ol>
    {% for comment in comments %}
    <li>{{ comment }}</li>
    {% endfor %}
</ol>

Where comments is a variable passed to template from the view. In others words, it's the value you obtain with comments = one_post.comment_set.all()