Django - minimal form

Posted under » Django on 6 May 2021

Let’s update our poll detail template (“polls/detail.html”) from the last tutorial, so that the template contains an HTML <form> element:

<h1>{{ question.question_text }}</h1>

{% if error_message %}<p><strong>{{ error_message }}</strong></p>{% endif %}

<form action="{% url 'vote' question.id %}" method="post">
{% csrf_token %}
{% for choice in question.choice_set.all %}
    <input type="radio" name="choice" id="choice{{ forloop.counter }}" value="{{ choice.id }}">
    <label for="choice{{ forloop.counter }}">{{ choice.choice_text }}</label><br>
{% endfor %}
<input type="submit" value="Vote">
</form>

• The above template displays a radio button for each question choice. The value of each radio button is the associated question choice’s ID. The name of each radio button is "choice".
• We set the form’s action to {% url 'vote' question.id %}, and we set method="post".
• forloop.counter indicates how many times the for tag has gone through its loop.
• Since we’re creating a POST form (which can have the effect of modifying data), we need to worry about Cross Site Request Forgeries. All POST forms that are targeted at internal URLs should use the {% csrf_token %} template tag.

Remember, we created a URLconf for the polls application that includes this line:

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

Now, let’s create a Django view that handles the submitted data. Add the following to polls/views.py:

from django.http import HttpResponse, HttpResponseRedirect
from django.shortcuts import get_object_or_404, render
from .models import Choice, Question
from django.urls import reverse

def vote(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    try:
        selected_choice = question.choice_set.get(pk=request.POST['choice'])
    except (KeyError, Choice.DoesNotExist):
        # Redisplay the question voting form.
        return render(request, 'polls/detail.html', {
            'question': question,
            'error_message': "You didn't select a choice.",
        })
    else:
        selected_choice.votes += 1
        selected_choice.save()
        # Always return an HttpResponseRedirect after successfully dealing
        # with POST data. This prevents data from being posted twice if a
        # user hits the Back button.
	return HttpResponseRedirect(reverse('polls:results', args=(question.id,)))

Please note that there is only one POST var that is being called. Please also read Forms CGI if you want more than one POST var.

• request.POST is a dictionary-like object that lets you access submitted data by key name. In this case, request.POST['choice'] returns the ID of the selected choice, as a string. request.POST values are always strings.
• Note that Django also provides request.GET for accessing GET data in the same way – but we’re explicitly using request.POST in our code, to ensure that data is only altered via a POST call.
• request.POST['choice'] will raise KeyError if choice wasn’t provided in POST data. The above code checks for KeyError and redisplays the question form with an error message if choice isn’t given.
• After incrementing the choice count, the code returns an HttpResponseRedirect rather than a normal HttpResponse. HttpResponseRedirect takes a single argument: the URL to which the user will be redirected (see the following point for how we construct the URL in this case).
• We are using the reverse() function in the HttpResponseRedirect constructor in this example. This function helps avoid having to hardcode a URL in the view function. It is given the name of the view that we want to pass control to and the variable portion of the URL pattern that points to that view. This reverse() call will return a string like

'/polls/3/results/'

In the template tutorial, request is an HttpRequest object

detail(request=, question_id=34)

The question_id=34 part comes from <int:question_id>. Using angle brackets “captures” part of the URL and sends it as a keyword argument to the view function. The :question_id> part of the string defines the name that will be used to identify the matched pattern, and the <int: part is a converter that determines what patterns should match this part of the URL path

After somebody votes in a question, the vote() view redirects to the results page for the question. Let’s write that views.py:

def results(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    return render(request, 'polls/results.html', {'question': question})

and let's do the polls/results.html.

<h1>{{ question.question_text }}</h1>

<ul>
{% for choice in question.choice_set.all %}
    <li>{{ choice.choice_text }} -- {{ choice.votes }} vote{{ choice.votes|pluralize }}</li>
{% endfor %}
</ul>

<a href="{% url 'polls:detail' question.id %}">Vote again?</a>

Now, go to /polls/1/ in your browser and vote in the question. You should see a results page that gets updated each time you vote. If you submit the form without having chosen a choice, you should see the error message.

let’s use Django’s own database API and use the API for our views.