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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
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Annotate in Models

In Django, the annotate() function is used to add computed fields (also known as annotations) to each object in a queryset. These computed fields are not stored in the database but are calculated on-the-fly for each object in the queryset based on the data retrieved from the database. The annotate() function is particularly useful when you want to perform aggregate calculations, add derived fields, or apply expressions to your queryset results.

Key Points:

  1. Non-Destructive: The annotate() function does not modify the original queryset; it returns a new queryset with the additional annotated fields.
  2. Computed Fields: You can use various functions, expressions, and aggregations within the expression argument to compute the value of the annotated field. Common functions include F() expressions, Value(), Concat(), Count(), Sum(), Avg(), and more.

Lets see with an example. You want to get the Persons with an additional field named, full_name which should concatenate the value first_name and last_name,

from django.db.models.functions import Concat
Person.objects.annotate(full_name=Concat('first_name', 'last_name')).values()

alt textHere an additional field, full_name is added and returned along with the queryset. This change is not done in the database.

If you want to separate the first_name and last_name by space, in the full_name field, then you would need to do it like this :

from django.db.models import Value
Person.objects.annotate(full_name=Concat('first_name', Value(' '),'last_name')).values()

alt text Conditional logic, as well can be applied inside the annotate() function,

from django.db.models import Case, When, IntegerField, Value
Person.objects.annotate(check_field=Case(When(birth_date__year__lt=1960, then=Value(1)),When(birth_date__year__lt=1990, then=Value(2)), default=Value(3),output_field=IntegerField())).values()

alt text Here, based on the condition of the birth year, the check_field value will be determined.


The `annotate()` function is a powerful tool for adding calculated fields to your querysets, allowing you to perform various data transformations and aggregations without modifying your database schema. It is commonly used in Django when you need to present data in a more informative or structured manner in your views and templates.
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