Django

Django is a popular open-source web framework written in Python. It follows the Model-View-Controller (MVC) architectural pattern, which separates the application code into different layers for better organization and management in a similar way that Apex follows.

The Django framework

Django's Database Abstraction Layer


from django.db import models

class Blog(models.Model):
    name = models.CharField(max_length=100)
    tagline = models.TextField()

    def __str__(self):
        return self.name

Django's URL Dispatcher


from django.urls import path

from . import views

urlpatterns = [
    path('', views.index, name='index'),
    path('product/create/', views.create, name='create'),
    path('product/created/', views.created, name='created'),
    path('', views.search, name='search'),
]

Django's Form Handling


from django import forms

class ContactForm(forms.Form):
    name = forms.CharField()
    message = forms.CharField(widget=forms.Textarea)

Django's Middleware Support


class SimpleMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        response = self.get_response(request)
        return response

Standard search request vs. Q object


from django.shortcuts import render
from .models import Product
from communications.models import Communication

def search(request):
    query = request.GET.get('q')
    if query:
        products = Product.objects.filter(code__icontains=query)
        communications = Communication.objects.filter(description__icontains=query)
    else:
        products = Product.objects.all()
        communications = Communication.objects.all()

    return render(request, 'search/search.html', {
        'query': query,
        'products': products,
        'communications': communications,
    })

Django's Q objects can be used when complex queries are required. Q objects can be used to combine queries with the logical operators | (OR) and & (AND) and the logical negation operator ~. They can be enclosed in parentheses to control the order of evaluation. Let's say you want to search both in 'name' and 'description' fields of a model. You can do it like this:


from django.shortcuts import render
from .models import Product
from communications.models import Communication
from django.db.models import Q

def search(request):
    query = request.GET.get('q')
    if query:
        products = Product.objects.filter(
            Q(name__icontains=query) |
            Q(description__icontains=query)
        )
        communications = Communication.objects.filter(
            Q(description__icontains=query)
        )
    else:
        products = Product.objects.all()
        communications = Communication.objects.all()

    return render(request, 'search/search.html', {
        'query': query,
        'products': products,
        'communications': communications,
    })

Most Asked Questions about Django

What are Django Middlewares and how can they be used?

Middleware is a framework of hooks into Django's request/response processing. It's a light, low-level plugin system for globally altering Django's input or output. It's a series of hooks into Django's request/response processing. It provides a way to process requests and responses globally before they reach the view or after they leave the view. Each middleware component is responsible for doing some specific function. For example, Django includes a middleware component, AuthenticationMiddleware, that associates users with requests using sessions.

A custom middleware can be created by defining a class with methods process_request(request) and/or process_response(request, response). These methods will be executed on every request before the view is called and on every response before it's returned to the client.

Can Django handle multiple databases? If so, how does it do it?

Yes, Django can handle multiple databases. Django provides a way for you to divide your queries across multiple databases. By default, it uses the 'default' database, but you can specify any other database when making a query. The DATABASES setting in Django must be configured with keys for each database connection. The key 'default' is required.


DATABASES = {
  'default': {
    ...
  },
  'extra_db': {
    ...
  }
}

To use one of these databases, you can use the using() method on a QuerySet object:


MyModel.objects.using('extra_db').all()

Django also includes a database router facility that lets you implement more complex database routing schemes for reading and writing data. The router can be used to decide which database should receive a particular query for reading or writing data.

What is the Django ORM, and how does it compare to SQL and other Python ORMs like SQLAlchemy?

The Django ORM (Object-Relational Mapping) is a component of Django that provides an abstract layer to work with databases. It allows you to create, retrieve, update, and delete records in your database using Python code instead of writing SQL queries. Compared to raw SQL, the Django ORM provides a higher-level, more Pythonic abstraction. It makes database operations easier to perform and the code easier to read and maintain. It also provides an extra layer of security by preventing SQL injection attacks.

Compared to SQLAlchemy, another popular Python ORM, Django's ORM is generally easier to use and more "batteries-included". It favors convention over configuration and comes with a lot of built-in features that make it easy to do common tasks. SQLAlchemy, on the other hand, is more flexible and powerful. It provides more control over the SQL and database schema, supports more complex queries and transactions, and has more options for configuring the ORM behavior. It's also database agnostic, meaning it can work with a wider variety of SQL databases compared to Django's ORM. However, this flexibility comes at the cost of increased complexity and a steeper learning curve.