Database Functions in Django
Last Updated :
15 Apr, 2024
In Django, database functions play an important role in querying, manipulating, and managing data stored in your application's database. In this article, we will learn about database functions in Django.
What are Database Functions in Django?
In Django, functions such as annotate, aggregate, and filter make it easier to work with data in the database. Annotate lets you add custom fields to the data you retrieve, aggregate helps you calculate summary values like averages or counts, and filter allows you to refine your queries based on specific conditions.
Implementation of Database Functions in Django
Below is the implementation of database functions in Django in Python:
Starting the Project Folder
django-admin startproject core
cd core
To start the app use this command
python manage.py startapp home
Now add this app to the ‘settings.py’
INSTALLED_APPS = [
"django.contrib.admin",
"django.contrib.auth",
"django.contrib.contenttypes",
"django.contrib.sessions",
"django.contrib.messages",
"django.contrib.staticfiles",
"home",
]
File Structure
Setting Necessary Files
models.py: Below code defines the structure of the database tables using Django's ORM (Object-Relational Mapping). In this case, there are two models: Author and Post. An Author has a name, and a Post has a title, content, author (linked to an Author), and creation timestamp.
Python3
class Author(models.Model):
name = models.CharField(max_length=100)
def __str__(self):
return self.name
class Post(models.Model):
title = models.CharField(max_length=200)
content = models.TextField()
author = models.ForeignKey(Author, on_delete=models.CASCADE)
created_at = models.DateTimeField(auto_now_add=True)
def __str__(self):
return self.title
views.py: Django view function post_list retrieves all posts and optionally filters them by author. It also calculates the total number of posts and authors with their respective post counts. The view then renders a template named 'post.html', passing the posts, authors, authors_with_posts, and total_posts as context variables..
Python3
from django.shortcuts import render
from home.models import Post
from django.db.models import Count
def post_list(request):
author_filter = request.GET.get('author', None)
posts = Post.objects.all()
if author_filter:
posts = posts.filter(author__name=author_filter)
authors_with_posts = Post.objects.values('author__name').annotate(num_posts=Count('id'))
total_posts = Post.objects.count()
# Extract the authors from authors_with_posts
authors = [author_with_posts['author__name'] for author_with_posts in authors_with_posts]
return render(request, 'post.html', {
'posts': posts,
'authors': authors, # Pass the authors instead of authors_with_posts
'authors_with_posts': authors_with_posts,
'total_posts': total_posts
})
home/urls.py: These files define the URL patterns for the Django application
Python
from django.urls import path
from . import views
urlpatterns = [
path('', views.post_list, name='post_list'),
]
core/urls.py : These files define the URL patterns for the Django application
Python3
from django.contrib import admin
from django.urls import path, include
urlpatterns = [
path('admin/', admin.site.urls),
path('', include('home.urls')),
]
Creating GUI
templates/post.html : This HTML template displays a post list with filtering by author. It includes a form for filtering, total post count, posts per author, and filtered posts in a table format.
HTML
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Post List</title>
<style>
table {
width: 50%;
border-collapse: collapse;
margin-bottom: 20px;
}
th, td {
border: 1px solid #ddd;
padding: 8px;
text-align: left;
}
th {
background-color: #f2f2f2;
}
</style>
</head>
<body>
<h1>Post List</h1>
<form action="" method="get">
<label for="author_filter">Filter by Author:</label>
<select name="author" id="author_filter">
<option value="">All Authors</option>
{% for author in authors %}
<option value="{{ author }}" {% if author_filter == author %}selected{% endif %}>{{ author }}</option>
{% endfor %}
</select>
<button type="submit">Apply Filter</button>
</form>
<h2>Total Posts: {{ total_posts }}</h2>
<h2>Posts per Author:</h2>
<table>
<thead>
<tr>
<th>Author</th>
<th>Number of Posts</th>
</tr>
</thead>
<tbody>
{% for author_with_posts in authors_with_posts %}
<tr>
<td>{{ author_with_posts.author__name }}</td>
<td>{{ author_with_posts.num_posts }}</td>
</tr>
{% endfor %}
</tbody>
</table>
<h2>Filtered Posts:</h2>
<table>
<thead>
<tr>
<th>Title</th>
<th>Content</th>
<th>Author</th>
</tr>
</thead>
<tbody>
{% for post in posts %}
<tr>
<td>{{ post.title }}</td>
<td>{{ post.content }}</td>
<td>{{ post.author.name }}</td>
</tr>
{% endfor %}
</tbody>
</table>
</body>
</html>
admin.py : below, are the admin.py file where we register the models.
Python3
from django.contrib import admin
from home.models import *
# Register your models here.
admin.site.register(Author)
admin.site.register(Post)
Deployment of the Project
Run these commands to apply the migrations:
python3 manage.py makemigrations
python3 manage.py migrate
For create superuser use the below command.
python3 manage.py createsuperuser
Run the server with the help of following command:
python3 manage.py runserver
Output
Video Demonstration
Similar Reads
Django Function Based Views
Django is a Python-based web framework which allows you to quickly create web application without all of the installation or dependency problems that you normally will find with other frameworks. Django is based on MVT (Model View Template) architecture and revolves around CRUD (Create, Retrieve, Up
7 min read
List View - Function based Views Django
List View refers to a view (logic) to list all or particular instances of a table from the database in a particular order. It is used to display multiple types of data on a single page or view, for example, products on an eCommerce page. Django provides extra-ordinary support for List Views but let'
3 min read
DatabaseError in Django
In this article, we will elucidate the 'django.db.utils.DatabaseError' by explaining. We will delve into the reasons behind the occurrence of this error and explore various approaches to handle it effectively. What is 'django.db.utils.DatabaseError ' ?The 'django.db.utils.DatabaseError' is an except
4 min read
Django Transaction System with Database Updates
In today's digital age, transaction systems play a pivotal role in various industries, from e-commerce platforms to banking and beyond. These systems are responsible for handling financial operations, ensuring data accuracy, and providing a seamless user experience. One of the most powerful tools fo
4 min read
Update View - Function based Views Django
Update View refers to a view (logic) to update a particular instance of a table from the database with some extra details. It is used to update entries in the database for example, updating an article at geeksforgeeks. So Update view must display the old data in the form and let user update the data
4 min read
Detail View - Function based Views Django
Detail View refers to a view (logic) to display a particular instance of a table from the database with all the necessary details. It is used to display multiple types of data on a single page or view, for example, profile of a user. Django provides extra-ordinary support for Detail Views but let's
3 min read
Create View - Function based Views Django
Create View refers to a view (logic) to create an instance of a table in the database. It is just like taking an input from a user and storing it in a specified table. Django provides extra-ordinary support for Create Views but let's check how it is done manually through a function-based view. This
3 min read
Delete View - Function based Views Django
Delete View refers to a view (logic) to delete a particular instance of a table from the database. It is used to delete entries in the database for example, deleting an article at geeksforgeeks. So Delete view must show a confirmation message to the user and should delete the instance automatically.
3 min read
Function based Views - Django Rest Framework
Django REST Framework allows us to work with regular Django views. It facilitates processing the HTTP requests and providing appropriate HTTP responses. In this section, you will understand how to implement Django views for the Restful Web service. We also make use of the @api_view decorator. Before
13 min read
Working with Multiple Databases in Django
Django stands out as a powerful and versatile framework for building dynamic and scalable applications. One of its notable features is its robust support for database management, offering developers flexibility in choosing and integrating various database systems into their projects. In this article
3 min read