Extend your application

We've already completed all the different steps necessary for the creation of our website: we know how to write a model, URL, view and template. We also know how to make our website pretty.

Time to practice!

The first thing we need in our blog is, obviously, a page to display one post, right?

We already have a Post model, so we don't need to add anything to models.py.

Create a template link to a post's detail

We will start with adding a link inside blog/templates/blog/post_list.html file. Open it in the code editor, and so far it should look like this:

blog/templates/blog/post_list.html

{% extends 'blog/base.html' %}

{% block content %}
    {% for post in posts %}
        <article class="post">
            <time class="date">
                {{ post.published_date }}
            </time>
            <h2><a href="">{{ post.title }}</a></h2>
            <p>{{ post.text|linebreaksbr }}</p>
        </article>
    {% endfor %}
{% endblock %}

We want to have a link from a post's title in the post list to the post's detail page. Let's change <h2><a href="">{{ post.title }}</a></h2> so that it links to the post's detail page:

blog/templates/blog/post_list.html

<h2><a href="{% url 'post_detail' pk=post.pk %}">{{ post.title }}</a></h2>

Time to explain the mysterious {% url 'post_detail' pk=post.pk %}. As you might suspect, the {% %} notation means that we are using Django template tags. This time we will use one that will create a URL for us!

The post_detail part means that Django will be expecting a URL in blog/urls.py with name=post_detail

And how about pk=post.pk? pk is short for primary key, which is a unique identifier for each record in a database. Every Django model has a field which serves as its primary key, and whatever other name it has, it can also be referred to as "pk". Because we didn't specify a primary key in our Post model, Django creates one for us (by default, a field named "id" holding a number that increases for each record, i.e. 1, 2, 3) and adds it as a field to each of our posts. We access the primary key by writing post.pk, the same way we access other fields (title, author, etc.) in our Post object!

Now when we go to http://127.0.0.1:8000/ we will have an error (as expected, since we do not yet have a URL or a view for post_detail). It will look like this:

Create a URL to a post's detail

Let's create a URL in urls.py for our post_detail view!

We want our first post's detail to be displayed at this URL: http://127.0.0.1:8000/post/1/

Let's make a URL in the blog/urls.py file to point Django to a view named post_detail, that will show an entire blog post. Open the blog/urls.py file in the code editor, and add the line path('post/<int:pk>/', views.post_detail, name='post_detail'), so that the file looks like this:

blog/urls.py

from django.urls import path
from . import views

urlpatterns = [
    path('', views.post_list, name='post_list'),
    path('post/<int:pk>/', views.post_detail, name='post_detail'),
]

This part post/<int:pk>/ specifies a URL pattern – we will explain it for you:

• post/ means that the URL should begin with the word post followed by a /. So far so good.
• <int:pk> – this part is trickier. It means that Django expects an integer value and will transfer it to a view as a variable called pk.
• / – then we need a / again before finishing the URL.

That means if you enter http://127.0.0.1:8000/post/5/ into your browser, Django will understand that you are looking for a view called post_detail and transfer the information that pk equals 5 to that view.

OK, we've added a new URL pattern to blog/urls.py! Let's refresh the page: http://127.0.0.1:8000/ Boom! The server has stopped running again. Have a look at the console – as expected, there's yet another error!

command-line

    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 850, in exec_module
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "/Users/ola/django-tutorial/blog/urls.py", line 6, in <module>
    path('post/<int:pk>/', views.post_detail, name='post_detail'),
AttributeError: module 'blog.views' has no attribute 'post_detail'

Do you remember what the next step is? It's adding a view!

Add a post's detail view

This time our view is given an extra parameter, pk. Our view needs to catch it, right? So we will define our function as def post_detail(request, pk):. Note that this parameter must have the exact same name as the one we specified in urls (pk). Also note that omitting this variable is incorrect and will result in an error!

Now, we want to get one and only one blog post. To do this, we can use querysets, like this:

blog/views.py

Post.objects.get(pk=pk)

But this code has a problem. If there is no Post with the given primary key (pk) we will have a super ugly error!

We don't want that! But luckily Django comes with something that will handle that for us: get_object_or_404. In case there is no Post with the given pk, it will display much nicer page, the Page Not Found 404 page.

The good news is that you can actually create your own Page not found page and make it as pretty as you want. But it's not super important right now, so we will skip it.

OK, time to add a view to our views.py file!

In blog/urls.py we created a URL rule named post_detail that refers to a view called views.post_detail. This means that Django will be expecting a view function called post_detail inside blog/views.py.

We should open blog/views.py in the code editor and add the following code near the other from lines:

blog/views.py

from django.shortcuts import render, get_object_or_404

And at the end of the file we will add our view:

blog/views.py

def post_detail(request, pk):
    post = get_object_or_404(Post, pk=pk)
    return render(request, 'blog/post_detail.html', {'post': post})

Yes. It is time to refresh the page: http://127.0.0.1:8000/

It worked! But what happens when you click a link in blog post title?

Oh no! Another error! But we already know how to deal with it, right? We need to add a template!

Create a template for the post details

We will create a file in blog/templates/blog called post_detail.html, and open it in the code editor.

Enter the following code:

blog/templates/blog/post_detail.html

{% extends 'blog/base.html' %}

{% block content %}
    <article class="post">
        {% if post.published_date %}
            <time class="date">
                {{ post.published_date }}
            </time>
        {% endif %}
        <h2>{{ post.title }}</h2>
        <p>{{ post.text|linebreaksbr }}</p>
    </article>
{% endblock %}

Once again we are extending base.html. In the content block we want to display a post's published_date (if it exists), title and text. But we should discuss some important things, right?

{% if ... %} ... {% endif %} is a template tag we can use when we want to check something. (Remember if ... else ... from Introduction to Python chapter?) In this scenario we want to check if a post's published_date is not empty.

OK, we can refresh our page and see if TemplateDoesNotExist is gone now.

Yay! It works!

Share time!

Let's update our repository with the new features we have implemented.

command-line

$ git status
$ git checkout -b post-details
$ git add .
$ git status
$ git commit -m "Added view and template for detailed blog post as well as CSS for the site."
$ git push

Now create a pull request, review, merge, update local etc.