checkmark

Django

Introduction to Django

What is Django How Django Works Installation and setup Creating Your First Django Project File Structure in Django Project Manage.py file in Django

Configuration in Settings File

Database Configuration No SQL Database Configuration Template Configuration Static Folder Configuration Media Configuration Tailwind Configuration

Apps in Django

Introduction Creating an app Routing app with project Displaying Welcome Message Rendering Template

Manage.py Commands

Help Command RunServer Command Shell Command Flush Command Creating Custom Command

Registration and Authentication - Default User Model

Introduction and Project Setup for User Authentication Routing authentication app with project Creating home page Restricting access to web page Register User Logout User Login User Redirection to Login Page Handling Next in Login

Models in Django

Characteristics of Models Creating a Model Interactive Shell for Model Operations String Representation for Model Generating Dummy Data Retrieving Data From Models Filters in Model Exclude in Models Field Lookups Q expressions Retrieving Single Record Updating A Record Updating Multiple Records Overriding save() method Annotate in Models F expressions Order By in Models Retrieving specific columns Prefetch particular columns alone Custom Methods in Model Data Types in Models One-To-One Relationship One-To-Many Relationship Many-to-Many Relationship Meta Class in Models Unique Parameter Static Method in Models

A basic Notes App

Introduction and Setup Configuring Templates and Static Folder Creating an app Creating Model Adding sample notes Display Notes Adding Note through form Edit Notes Delete a Note Display Bug Update Admin Panel Register Note Model Customize Admin Page Editing Fields in List Downloading Notes as CSV file

Data Types in Models

Data Type Demo App creation Char Field Text Field Integer Field Float Field Decimal Field

College Event Registration Website

CampusConnect Introduction and Setup Configuring settings file for template, static and media files Setting up Tailwind Creating Custom User Model Creating Super User for CampusConnect Registering Custom User Model Search and Filter for User Model Serving Media Files During Development Categorizing Departments Linking Department with HOD Creating Abstract Model for Event Creating Model for Workshop Customizing Admin Page for Workshop Update in Model AbstractEvent Adding Instructor for Workshop Instructor Model Admin Page Adding Poster Field in Abstract Event Providing Access to HOD Access Update for HOD Restricting HOD Access to Particular Department AbstractEvent On Spot Registration Field Creating Workshop Object Creating and Linking Home Page Displaying Workshop on Home Page Styling Home Page Adding Workshop Detail Page Link Workshop Detail Page Workshop Detail Page Styling Workshop Instructor Details Workshop Detail Contact Contact Admin Page Many to Many Field for Contact Displaying Contact on Workshop Detail Page Adding Title for Workshop Detail Page Adding Gallery for Workshop Workshop Gallery Admin Page Displaying Gallery Images on Website Through Context Displaying Gallery Images on Website through template tags Authentication for users User Registration User Registration Submission Logout Functionality For User Login Functionality for User Model For Workshop Registration Workshop Registration Admin Page Register Workshop Function Register Button in Workshop Page Validations Before Workshop Registration Workshop Registration Closed Validaiton User Already Registered for Workshop Validation Workshop Registration Report From Admin Page Export using Library in Django Admin Extending Abstract Event for Hackathons
menu Back to Edkool

Q expressions

Q expressions in Django are a powerful feature that allow you to create complex database queries using logical operators. They are used to dynamically construct queries and apply conditional filters to QuerySets in a flexible and expressive way. One of the primary reasons for using Q expressions is to construct complex queries involving multiple conditions.

In order to use Q expressions, you first need to import it.

from django.db.models import Q

Consider a scenario where you want to get the name of Persons whose first_name either starts with J or starts with M, without using Q expressions you will write a code like this,

Person.objects.filter(first_name__startswith='J') | Person.objects.filter(first_name__startswith='M')

Using Q expressions, the above query can be changed as follows :

from django.db.models import Q
Person.objects.filter(Q(first_name__startswith='J') | Q(first_name__startswith='M'))

alt textThis eliminates the need to chain multiple filter() or exculde() statements.

Similarly, the & operator, can also be used in Q expressions. Consider a case where you want records whose first_name starts with M and last_name ends with s or who is born before 1960, then the code without Q expressions would be :

Person.objects.filter(first_name__startswith='M', last_name__endswith='s').values() | Person.objects.filter(birth_date__year__lte=1960).values()

Using Q expressions, the above query can be changed as follows :

Person.objects.filter((Q(first_name__startswith='M') & Q(last_name__endswith='s')) | Q(birth_date__year__lte=1960)).values()

alt text Q expressions also allow you to use the ~ operator for negation, making it straightforward to exclude() records that meet specific criteria. For example, getting records of Person who are not born in October. Without using Q expressions the code would be,

Person.objects.exclude(birth_date__month=10).values()

Using Q expressions, the above query can be changed as follows :

Person.objects.filter(~Q(birth_date__month=10)).values()

alt textThe negation ~ can similarly be combined with other & and | conditions.

Q expressions are invaluable when you need to build queries dynamically based on user input or other runtime conditions. They allow you to construct queries in a way that can change depending on the specific requirements, making your application more flexible.

from django.db.models import Q
firstname = 'Mi'
birth_month=8
q_objects = Q(first_name__icontains=firstname)
if birth_month:
    q_objects |= Q(birth_date__month=birth_month)
Person.objects.filter(q_objects).values()

alt text Using Q expressions can lead to more readable and maintainable code, especially when dealing with complex queries. They make it easier to express your query logic in a natural and organized way.

Previous Field Lookups
Next Retrieving Single Record