Django crash course

Reproduction step-by-step of this course "Python crash course"

Django crash course
- Steps
- Tutorial expansion
  - Create a REST API

Steps

Setup

Install pipenv

sudo -H pip3 install pipenv
Create pipenv dependencies file

pipenv shell
Install django in environment

pipenv install django
Create django pollster project

django-admin startproject pollster

These files are created
- pollster/
  - asgi.py
  - settings.py: contains django configuration (production secret key, database, tzconfig...)
  - urls.py: contains url managed by the application
  - wsgi.py
Run installed django environment (for testing)

cd pollster/ && python3 manage.py runserver
Run migrations (to create default database)

python3 manage.py migrate
Create app (polls)

python3 manage.py startapp polls
Add polls to apps

move to pollster/pollster/settings.py and add to INSTALLED_APPS the entry 'polls.apps.PollsConfig'

Define the model

We're then going to define the model for our poll applications. These entities will then be created into the database, when running the migration.

move to pollster/polls/models.py

Define models

class Question(models.Model):
    """
    Question represents a poll
    """
    question_text = models.CharField(max_length=256)
    pub_date = models.DateTimeField("publication date")

    def __str__(self) -> str:
        return self.question_text

class Choice(models.Model):
    """
    Choice represents a choice for a certain ``Question``
    """
    # If a question is deleted, all related choices are deleted -> `on_delete = models.CASCADE`
    question = models.ForeignKey(Question, on_delete=models.CASCADE)
    choice_text = models.CharField(max_length=256)
    votes = models.IntegerField(default=0)

    def __str__(self) -> str:
        return self.choice_text

Make migrations

run python manage.py makemigrations polls
Run migrations

as before python3 manage.py migrate

Add records

Run shell and add a new Question entity

python manage.py shell
>>> from django.utils import timezone
>>> from polls.models import Question, Choice
>>> q = Question(question_text = "What is your favourite Programming language?", pub_date=timezone.now())
>>> q.save()
>>> q.id
>>> q.question_text
>>> Questions.objects.all()

Add a new Choice

python manage.py shell
>>> q = Question.objects.get(pk = 1)
>>> q.choices.create(choice_text = "C/C++")
>>> q.choices.create(choice_text = "JavaScript")
>>> q.choices.create(choice_text = "Rust")
>>> q.choices.create(choice_text = "Python")
>>> q.choices.create(choice_text = "Java")
>>> q.choices.create(choice_text = "CSharp")
>>> q.choices.create(choice_text = "Go")
>>> q.choices.create(choice_text = "PHP")
>>> q.choices.create(choice_text = "Ruby")
>>> q.save()
>>> quit()

Enter admin area

Create super user

python manage.py createsuperuser
Username (leave blank to use '${USER}'): 
Email address: christian.visintin@*********
Password:
Password (again):
This password is too short. It must contain at least 8 characters.
Bypass password validation and create user anyway? [y/N]: y
Superuser created successfully.

Run server

python manage.py runserver
Go to admin page

from your browser: http://localhost:8000/admin
Access with your credentials

Add to administration a form to add polls

Move to pollster/polls/admin.py

Let's add models

from .models import Question, Choice

admin.site.register(Question)
admin.site.register(Choice)

Now you're finally able to add Questions and choices to the database.

Let's make it cooler

# Register your models here.
from .models import Question, Choice

class ChoiceInline(admin.TabularInline):
    model = Choice
    extra = 3 # Default choices entries

class QuestionAdmin(admin.ModelAdmin):
    fieldsets = [
        (None, {'fields': ['question_text']}),
        ('Date Information', {'fields': ['pub_date'], 'classes': ['collapse']}),
    ]
    inlines = [ChoiceInline]

#admin.site.register(Question)
#admin.site.register(Choice)
admin.site.register(Question, QuestionAdmin)

(Extra) add header and title for administration

# Set website header
admin.site.site_header = "Pollster Admin"
admin.site.site_title = "Pollster Admin Area"
admin.site.index_title = "Welcome to Pollster administration"

Create the first view

Move to pollster/polls/views.py
Show questions

Add index definition

from .models import Question, Choice

# Get questions and display then

def index(request):
    return render(request, 'polls/index.html')

Define url

Create pollster/polls/urls.py and type

from django.urls import path

# Import views
from . import views

# Give app a name
app_name = "polls"
urlpatterns = [
    path('', views.index, name='index') # /polls/index.html
]

Add polls url to pollster urls

Move to pollster/pollster/urls.py

and add change urlpatterns to:

# Add include
from django.urls import path, include
# ...
# Add here
urlpatterns = [
  path('admin/', admin.site.urls),
  path('polls/', include('polls.urls')),
]

Add templates folder in pollster/templates
Add index.html to pollster/templates/polls/index.html
Set templates as global folder

move to pollster/pollster/settings.py and to TEMPLATES add 'DIRS': [os.path.join(BASE_DIR, 'templates')],

Make HTML templates

Let's make base html template at pollster/templates/base.html

Extend base in pollster/templates/polls/index.html

{% extends 'base.html' %}
{% block content %}
  POLLS
{% endblock %}

Show questions in index

Move to pollster/polls/views.py

def index(request):
latest_question_list = Question.objects.order_by('-pub_date')[:5] # Max 5 and sort by pub date
context = {'latest_question_list': latest_question_list}
return render(request, 'polls/index.html', context=context)

Add implementation for index.html

{% extends 'base.html' %}
{% block content %}
  <h1 class="text-center mb-3">Poll questions</h1>
  {% if latest_question_list %}
    {% for question in latest_question_list %}
      <div class="card mb-3">
        <div class="card-body">
          <h2 class="lead">
            {{ question.question_text }}
          </h2>
          <a href="{% url 'polls:detail' question.id %}" class="btn btn-primary btn-sm">Vote now!</a>
          <a href="{% url 'polls:results' question.id %}" class="btn btn-secondary btn-sm">View results</a>
        </div>
      </div>
    {% endfor %}
  {% else %}
    <h2 class="text-center mb-3">No polls available</h2>
  {% endif %}
{% endblock %}

Let's implement details

Move to pollster/polls/views.py

def detail(request, question_id):
    """
    Show speicific question and choices
    """
    try:
        # Get question by id
        question = Question.objects.get(pk=question_id)
    except Question.DoesNotExist:
        # Return 404
        raise Http404
    context = {'question': question}
    return render(request, 'polls/detail.html', context=context)

Let's implement results

def results(request, question_id: int):
    """
    Show results for a question
    """
    question = get_object_or_404(Question, pk=question_id)
    context = {'question': question}
    return render(request, 'polls/results.html', context=context)

Add other pages to pollster/polls/urls.py

urlpatterns = [
    path('', views.index, name='index'), # /polls/index.html
    path('<int:question_id>', view=views.detail, name='detail'),
    path('<int:question_id>', view=views.results, name='results'),
    path('<int:question_id>/vote/', views.vote, name='vote'),
]

Add results.html and detail.html

Add vote

def vote(request, question_id: int):
    """
    Enregister the user vote
    """
    question = get_object_or_404(Question, pk=question_id)
    try:
        selected_choice = question.choices.get(pk=request.POST['choice'])
    except (KeyError, Choice.DoesNotExist):
        return render(request, 'polls/detail.html', {
            'question': question,
            'error_message': "You didn't select any choice"
        })
    else:
        # Increase choice counter and save
        selected_choice.votes += 1
        selected_choice.save()
        # Return results
        return HttpResponseRedirect(reverse('polls:results', args=(question_id,)))

Tutorial expansion

This part is not included in the django crash course video, but I included since I found it useful.

Create a REST API

Let's create a REST API to interact with the poll application. We'll implement the following methods

GET /polls/api/questions

which will return an object with all questions summary

[
    {
        "id": 1,
        "text": "What's your favourite programming language?"
    }
]

GET /polls/api/question/{ID}

which will return an object with the question details and choices

[
    {
        "id": 1,
        "text": "What's your favourite programming language?",
        "choices": [
            {
                "id": 1,
                "text": "Rust",
                "votes": 2
            },
            {
                "id": 2,
                "text": "C/C++",
                "votes": 1
            }
        ]
    }
]

POST /polls/api/vote/{QUESTION_ID}

which will enregister the vote for a certain poll

{
    "choice": 2
}

Let's see the implementation step-by-step.

Setup:

Install Django REST Framework
```
pip install djangorestframework
```
Tell Django we've installed the REST framework

Move to pollster/pollster/settings.py
```
INSTALLED_APPS = [
#...
'rest_framework',
]
```

Let's create the GET request

Add related_name to Choice in models:

Move to pollster/polls/models.py

class Choice(models.Model):
    """
    Choice represents a choice for a certain ``Question``
    """
    # If a question is deleted, all related choices are deleted -> `on_delete = models.CASCADE`
    question = models.ForeignKey(Question, related_name='choices', on_delete=models.CASCADE)
    #...

Create serializers

move to pollster/polls/serializers.py

# Import serializers from REST framework
from rest_framework import serializers
# Import our models
from .models import Question, Choice

class ChoiceSerializer(serializers.ModelSerializer):
    class Meta:
        model = Choice
        fields = ('choice_text', 'votes', 'id')

class QuestionBriefSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = Question
        fields = ('question_text', 'pub_date')

class QuestionSerializer(serializers.HyperlinkedModelSerializer):
    # Add choices to relations and serialize it using the `ChoiceSerializer`
    choices = ChoiceSerializer(many=True)
    class Meta:
        model = Question
        fields = ('question_text', 'pub_date', 'choices')

Display data in views

move to pollster/polls/views.py

from rest_framework.response import Response
from rest_framework.decorators import api_view
from .serializers import QuestionSerializer, QuestionBriefSerializer
#...
@api_view(['GET'])
def questionList(request):
    questions = Question.objects.all().order_by('pub_date')
    serializer = QuestionBriefSerializer(questions, many=True) # Many indicates whether we want 1 or more elements
    return Response(serializer.data)

@api_view(['GET'])
def questionDetail(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    serializer = QuestionSerializer(question, many=False) # Many indicates whether we want 1 or more elements
    return Response(serializer.data)

Add URLs and router

Move to pollster/polls/urls.py

from django.urls import path

# Import views
from . import views

# Give app a name
app_name = "polls"
urlpatterns = [
    path('', views.index, name='index'), # /polls/index.html
    path('<int:question_id>/', views.detail, name='detail'),
    path('<int:question_id>/results', views.results, name='results'),
    path('<int:question_id>/vote/', views.vote, name='vote'),
    path('api/questions/', views.questionList, name='questions'),
    path('api/question/<int:question_id>/', views.questionDetail, name="question"),
]

Now you should finally be able to perform a GET to http://localhost:8000/polls/api/questions

Let's implement the vote POST method.

Add request to view

@api_view(['POST'])
@parser_classes([JSONParser])
def questionVote(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    print(request.data)
    try:
        selected_choice = question.choices.get(pk=request.data['choice'])
    except (KeyError, Choice.DoesNotExist):
        raise Http404
    else:
        # Increase choice counter and save
        selected_choice.votes += 1
        selected_choice.save()
    # Return updated question
    serializer = QuestionSerializer(question, many=False) # Many indicates whether we want 1 or more elements
    return Response(serializer.data)

Add URL

path('api/vote/<int:question_id>', views.questionVote, name="vote"),

And that's all.

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