Most Popular Django Interview Questions
and Answers

How to check if user instance is admin django permissions?

The is_superuser property in User model, designates that this user has all permissions without explicitly assigning them.

class UserAdmin(BaseUserAdmin):
    ...
    def has_add_permission(self, request, obj=None):
        return request.user.is_superuser

    def has_delete_permission(self, request, obj=None):
        return request.user.is_superuser

What is a "slug" in Django?

A "slug" is a way of generating a valid URL, generally using data already obtained. For instance, a slug uses the title of an article to generate a URL. I advise to generate the slug by means of a function, given the title (or another piece of data), rather than setting it manually. An example:

<title> The 46 Year Old Virgin </title>
<content> A silly comedy movie </content>
<slug> the-46-year-old-virgin </slug>

Now let's pretend that we have a Django model such as:

class Article(models.Model):
    title = models.CharField(max_length=100)
    content = models.TextField(max_length=1000)
    slug = models.SlugField(max_length=40)
    

How would you reference this object with a URL and with a meaningful name? You could for instance use Article.id so the URL would look like this:

www.example.com/article/23

Or, you might want to reference the title like this:

www.example.com/article/The 46 Year Old Virgin

Since spaces aren't valid in URLs, they must be replaced by %20, which results in:

www.example.com/article/The%2046%20Year%20Old%20Virgin

Both attempts are not resulting in very meaningful, easy-to-read URL. This is better:

www.example.com/article/the-46-year-old-virgin

In this example, the-46-year-old-virgin is a slug: it is created from the title by down-casing all letters, and replacing spaces by hyphens -

What is the Django ORM, and how does it work?

The Django ORM (Object-Relational Mapping) is a powerful tool for interacting with databases in Django applications. It allows developers to define database models using Python classes and methods, which are then translated into database tables and fields automatically. The ORM provides a high-level, abstracted interface for working with databases, which makes it easy to perform common database operations, such as creating, reading, updating, and deleting records.

What is a Django middleware and how is it used?

A Django middleware is a component that sits between the web server and the view function and can perform operations on incoming requests or outgoing responses. Middleware can be used to perform tasks such as authentication, caching, logging, or modifying headers.

What is a Django signal? Explain with an example

Django signals are a way of allowing decoupled applications to get notified when certain actions occur elsewhere in the application. They provide a means of broadcasting messages within your application without requiring a specific recipient.

For example, when a new user is created in Django, you might want to perform some additional tasks such as sending a welcome email or creating a profile for the user. Instead of adding this functionality directly to the user creation code, you can use signals to trigger these additional tasks whenever a new user is created.

Here's an example of using signals in Django:

from django.db.models.signals import post_save
from django.dispatch import receiver
from django.contrib.auth.models import User
from myapp.models import UserProfile

@receiver(post_save, sender=User)
def create_profile(sender, instance, created, **kwargs):
    if created:
        UserProfile.objects.create(user=instance)

@receiver(post_save, sender=User)
def save_profile(sender, instance, **kwargs):
    instance.profile.save()

In this example, we define two signal handlers using the @receiver decorator. The first handler create_profile creates a new UserProfile object whenever a new User object is created. The second handler save_profile saves the UserProfile object whenever the User object is saved.

We attach these signal handlers to the post_save signal of the User model using the @receiver decorator. Whenever a User object is saved, these signal handlers will be called and perform the required actions.

How does Django handle database migrations?

Django is a popular web framework that comes with an integrated Object-Relational Mapping (ORM) system for database interaction. Django handles database migrations through its built-in migration framework.

When any changes are made to the Django models, such as adding or removing fields, those changes needs to be applied on your database schema. The migration framework allows you to do this in a organized way by keeping track of each change and its dependencies.

Here are the main steps in the Django database migration process:

1. Create an initial migration: The first time you use Django's migration framework, you need to create an initial migration. This migration will contain the current state of your database schema.
2. Define your models: You define your Django models in your code, using the Django ORM. Each model corresponds to a database table, and each field in the model corresponds to a column in that table.
3. Create a migration for each change: When you make changes to your models, you create a new migration to reflect those changes. This can be done using the makemigrations command. Each migration file contains the instructions for applying or reversing the changes.
4. Apply the migrations: Once you've created the migration files, you need to apply them to your database using the migrate command. Django will read the migration files in order and apply the changes to the database schema.
5. Rollback migrations: If you need to revert a migration, you can use the migrate command with the -reverse option to undo the changes made by the most recent migration.

How do you define a URL pattern in Django?

To define a URL pattern in Django, we need to create a URL configuration file in our main application directory. This file is usually called urls.py.

Here's an example

from django.urls import path
from . import views

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

In this example, we import the path function from django.urls and the views module from our app. We define a list of URL patterns, each of which is represented by a path object.

Each path object takes two arguments: the URL pattern, and the view function that should be called when the URL pattern is matched. The name argument is optional, but it's a good idea to include it because it allows you to refer to the URL pattern by name in your templates and other parts of your code.

In the example above, we have four URL patterns:

• '': This matches the root URL (/) and calls the home view function.
• 'about/': This matches the /about/ URL and calls the about view function.
• 'post/<int:pk>/': This matches URLs of the form /post/1/, /post/2/, etc., where the number after post/ is passed to the view function as a variable named pk. The view function for this URL pattern is post_single.

Note that the order of the URL patterns defined in this file is very important. Django will try to match the URL patterns in the order they appear in the list, so more specific patterns should be listed before more general ones.

How do you define a model in Django?

To define a model in Django, you need to create a Python class that inherits from the django.db.models.Model class.

Here's an example of a simple model that represents a blog post:

from django.db import models

class Post(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()
    published_date = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return self.title

In this example, we have defined a Post model with three fields: title, content, and published_date. Each field is defined as an instance of a Field class from the django.db.models module.

The title field is a CharField with a maximum length of 200 characters, while the content field is a TextField that can hold an unlimited amount of text. The pub_date field is a DateTimeField that automatically sets the date and time when the record is created, using the auto_now_add=True parameter.

We also define a __str__ method to provide a human-readable representation of the model instance. In this case, we simply return the title of the post.

Once you've defined your model, you need to create a database table to store the data. You can do this by running the following commands.

python manage.py makemigrations
python manage.py migrate

What is Django and how does it differ from other web frameworks?

Django is a one of the most popular Python web framework that follows the model-template-view (MTV) architectural pattern. It was created to make web development easier and more efficient by providing built-in components and best practices for common web development tasks, such as handling requests and responses, database interactions, URL routing, authentication, and more.

Django is often compared to other popular web frameworks, such as Flask, Pyramid, and Ruby on Rails. Here are some ways that Django differs from these other frameworks:

1. Django is a opinionated framework: Django framework comes with a lot of built-in components to build a robust web application. It adheres to certain conventions for how things should be done. Depending on your point of view, this can be a strength or a weakness.
2. Stiff learning curve: Because Django is a more fully-featured framework, it can take longer to learn than some of the simpler frameworks like Flask. However, once you’re hands on with Django, you can be more productive because many common tasks are available out of the box.
3. Django is built for larger complex projects: While Django can be used for small projects, it really shines when used for larger, more complex web applications that require a lot of functionality and scalability. Django's built-in components, such as the ORM, admin interface, and authentication system, make it easy to build and manage large applications.
4. Django has better documentation: Django has excellent documentation that is both comprehensive and easy to understand. This can make it easier for developers to learn the framework and get up to speed quickly.

Overall, Django is a powerful and versatile web framework that is well-suited for building complex web applications. While it may take some time to learn, it can help developers be more productive in the long run by providing a solid foundation and best practices for building web applications.

How to Combine Multiple QuerySets in Django?

In Django, you can combine multiple querysets from different models or the same model using the union(), difference(), or intersection() methods. The union() method is the most common way to merge multiple querysets.

Here's an example of how you can use union() to combine querysets:

from django.db.models import Q
from myapp.models import MyModel1, MyModel2

queryset1 = MyModel1.objects.filter(some_field=some_value)
queryset2 = MyModel2.objects.filter(another_field=another_value)
queryset_combined = queryset1.union(queryset2)

Keep in mind that union(), difference(), and intersection() only work on querysets from the same model or models with the same fields. If you need to combine querysets from models with different fields, you can use the chain() function from the itertools library, but the result will be an iterable, not a queryset.

Here's an example of using chain():

from itertools import chain
from myapp.models import MyModel1, MyModel2

queryset1 = MyModel1.objects.filter(some_field=some_value)
queryset2 = MyModel2.objects.filter(another_field=another_value)
combined_iterable = chain(queryset1, queryset2)

Note that the chain() method does not allow to perform further queryset operations (like filtering, ordering, etc.) on the combined iterable. If you need to perform further operations on the combined result, you can convert it into a list and then use Python's built-in functions or list comprehensions.

What is related_name used for in Django Model Mapping?

The related_name attribute is used in Django Model field definitions, specifically for ForeignKey, OneToOneField, and ManyToManyField relationships, to specify the reverse relation from the related model back to the model that defines the relationship.

By default, Django creates a reverse relation using the lowercased model name followed by _set (e.g., modelname_set).

The related_name attribute allows you to provide a custom name for this reverse relation, making your code more readable and understandable.

Here's an example:

from django.db import models

class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.ForeignKey(Author, on_delete=models.CASCADE, related_name='books')

In this example, we have an Author model and a Book model with a ForeignKey relationship from Book to Author. By specifying related_name='books' in the ForeignKey definition, we create a reverse relation from Author to Book using the name 'books' instead of the default 'book_set'.

With the related_name defined, you can query the related objects like this:

author = Author.objects.get(name='John Doe')
books_by_author = author.books.all()

This is more readable than using the default reverse relation:

books_by_author = author.book_set.all()

If you have multiple ForeignKey or ManyToManyField relationships between the same models, you must provide a unique related_name for each relationship to avoid naming conflicts.