Django Views and URL Routing

Django Views

Django Views are one of the vital participants of MVT Structure of Django. As per Django Documentation, A view function is a Python function that takes a Web request and returns a Web response. This response can be the HTML contents of a Web page, or a redirect, or a 404 error, or an XML document, or an image, anything that a web browser can display.

Django views are part of the user interface — they usually render the HTML/CSS/Javascript in your Template files into what you see in your browser when you render a web page. (Note that if you’ve used other frameworks based on the MVC (Model-View-Controller), do not get confused between Django views and views in the MVC paradigm. Django views roughly correspond to controllers in MVC, and Django templates to views in MVC.)

Django View Example

Illustration of How to create and use a Django view using an Example. Consider a project named geeksforgeeks having an app named geeks.

After you have a project ready, we can create a view in geeks/views.py,

# import Http Response from django
from django.http import HttpResponse
# get datetime
import datetime

# create a function
def geeks_view(request):
    # fetch date and time
    now = datetime.datetime.now()
    # convert to string
    html = "Time is {}".format(now)
    # return response
    return HttpResponse(html)

Let’s step through this code one line at a time:

First, we import the class HttpResponse from the django.http module, along with Python’s datetime library.
Next, we define a function called geeks_view. This is the view function. Each view function takes an HttpRequest object as its first parameter, which is typically named request.
The view returns an HttpResponse object that contains the generated response. Each view function is responsible for returning an HttpResponse object.
For more info on HttpRequest and HttpResponse visit – Django Request and Response cycle – HttpRequest and HttpResponse Objects

Let’s get this view to working, in geeks/urls.py,


from django.urls import path

# importing views from views..py
from .views import geeks_view

urlpatterns = [
    path('', geeks_view),
]

Now, visit http://127.0.0.1:8000/,

To check how to make a basic project using MVT (Model, View, Template) structure of Django, visit Creating a Project Django.

Types of Views

Django views are divided into two major categories:-

Function-Based Views
Class-Based Views

Function Based Views

Function based views are written using a function in python which receives as an argument HttpRequest object and returns an HttpResponse Object. Function based views are generally divided into 4 basic strategies, i.e., CRUD (Create, Retrieve, Update, Delete). CRUD is the base of any framework one is using for development.

Function based view Example –

Let’s Create a function-based view list view to display instances of a model. Let’s create a model of which we will be creating instances through our view. In geeks/models.py,

# import the standard Django Model
# from built-in library
from django.db import models

# declare a new model with a name "GeeksModel"
class GeeksModel(models.Model):

    # fields of the model
    title = models.CharField(max_length = 200)
    description = models.TextField()

    # renames the instances of the model
    # with their title name
    def __str__(self):
        return self.title

After creating this model, we need to run two commands in order to create Database for the same.


Python manage.py [makemigrations](https://www.geeksforgeeks.org/django-app-model-python-manage-py-makemigrations-command/)
Python manage.py [migrate](https://www.geeksforgeeks.org/django-manage-py-migrate-command-python/)

Now let’s create some instances of this model using shell, run form bash,

Python manage.py shell Enter following commands

>>> from geeks.models import GeeksModel
>>> GeeksModel.objects.create(
                       title="title1",
                       description="description1").save()
>>> GeeksModel.objects.create(
                       title="title2",
                       description="description2").save()
>>> GeeksModel.objects.create(
                       title="title2",
                       description="description2").save()

Now if you want to see your model and its data in the admin panel, then you need to register your model. Let’s register this model. In geeks/admin.py,

from django.contrib import admin
from .models import GeeksModel
# Register your models here.
admin.site.register(GeeksModel)

Now we have everything ready for the back end. Verify that instances have been created from http://localhost:8000/admin/geeks/geeksmodel/

Let’s create a view and template for the same. In geeks/views.py,


from django.shortcuts import render

# relative import of forms
from .models import GeeksModel

def list_view(request):
    # dictionary for initial data with 
    # field names as keys
    context ={}

    # add the dictionary during initialization
    context["dataset"] = GeeksModel.objects.all()

    return render(request, "list_view.html", context)

Create a template in templates/list_view.html,

<div class="main">

    {% for data in dataset %}.

    {{ data.title }}<br/>
    {{ data.description }}<br/>
    <hr/>

    {% endfor %}

</div>

Let’s check what is there on http://localhost:8000/

Similarly, function based views can be implemented with logics for create, update, retrieve and delete views. Django CRUD (Create, Retrieve, Update, Delete) Function Based Views :-

Class Based Views

Class-based views provide an alternative way to implement views as Python objects instead of functions. They do not replace function-based views, but have certain differences and advantages when compared to function-based views:

Organization of code related to specific HTTP methods (GET, POST, etc.) can be addressed by separate methods instead of conditional branching.
Object oriented techniques such as mixins (multiple inheritance) can be used to factor code into reusable components. Class-based views are simpler and efficient to manage than function-based views. A function-based view with tons of lines of code can be converted into class-based views with few lines only. This is where Object-Oriented Programming comes into impact.

Class based view Example – In geeks/views.py,

from django.views.generic.list import ListView
from .models import GeeksModel

class GeeksList(ListView):

    # specify the model for list view
    model = GeeksMode

Now create a URL path to map the view. In geeks/urls.py,

from django.urls import path

# importing views from views..py
from .views import GeeksList
urlpatterns = [
    path('', GeeksList.as_view()),
]

<ul>
    <!-- Iterate over object_list -->
    {% for object in object_list %}
    <!-- Display Objects -->
    <li>{{ object.title }}</li>
    <li>{{ object.description }}</li>

    <hr/>
    <!-- If objet_list is empty  -->
    {% empty %}
    <li>No objects yet.</li>
    {% endfor %}
</ul>

Let’s check what is there on http://localhost:8000/

Django URLS

Prerequisites: Views in Django In Django, views are Python functions which take a URL request as parameter and return an HTTP response or throw an exception like 404. Each view needs to be mapped to a corresponding URL pattern. This is done via a Python module called URLConf(URL configuration)

Let the project name be myProject. The Python module to be used as URLConf is the value of ROOT_URLCONF in myProject/settings.py. By default this is set to 'myProject.urls'. Every URLConf module must contain a variable urlpatterns which is a set of URL patterns to be matched against the requested URL. These patterns will be checked in sequence, until the first match is found. Then the view corresponding to the first match is invoked. If no URL pattern matches, Django invokes an appropriate error handling view.

Including other URLConf modules It is a good practice to have a URLConf module for every app in Django. This module needs to be included in the root URLConf module as follows:

from django.contrib import admin 
from django.urls import path, include 

urlpatterns = [ 
    path('admin/', admin.site.urls), 
    path('', include('books.urls')), 
]

This tells Django to search for URL patterns in the file books/urls.py.

URL patterns

Here’s a sample code for books/urls.py:

from django.urls import path 
from . import views 

urlpatterns = [ 
    path('books/<int:pk>/', views.book_detail), 
    path('books/<str:genre>/', views.books_by_genre), 
    path('books/', views.book_index), 
]

For example,

A URL request to /books/crime/ will match with the second URL pattern. As a result, Django will call the function views.books_by_genre(request, genre = "crime").
Similarly a URL request /books/25/ will match the first URL pattern and Django will call the function views.book_detail(request, pk =25).

Here, int and str are path convertors and capture an integer and string value respectively.

Path convertors: The following path convertor types are available in Django

int – Matches zero or any positive integer.
str – Matches any non-empty string, excluding the path separator(‘/’).
slug – Matches any slug string, i.e. a string consisting of alphabets, digits, hyphen and under score.
path – Matches any non-empty string including the path separator(‘/’)
uuid – Matches a UUID(universal unique identifier).

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