Django Models

Django models are a fundamental component of Django web applications, offering a simplified and pythonic way to define the structure of your data. Acting as Python classes, Django models enable seamless interactions with the underlying database. With models, developers can work with data more intuitively, abstracting away the complexities of SQL queries and database management.

• Each model is a Python class that subclasses django.db.models.Model.

• Each attribute of the model represents a database field.

Example :

from django.db import models

class Post(models.Model):
    title = models.CharField(max_length=200)
    description = models.TextField()

    def __str__(self):
        return self.title

In this example, the "Post" model defines fields for title, description, and image. The CharField represents a character field with a maximum length of 200 characters, while the TextField represents a longer text field. The __str__ method returns the title of the post for better readability.

Corresponding schema

Databases in Django

In Django, the default database is set up to use SQLite as the database engine.

• In your project's "settings.py" file, the default database configuration is typically set up like this:

    DATABASES = {
        'default': {
            'ENGINE': 'django.db.backends.sqlite3',   # SQLite database engine
            'NAME': BASE_DIR / 'db.sqlite3',          # Database file path
        }
    }
  

Explanation of the configuration:

1. ENGINE: This specifies the database engine to be used, which is set to 'django.db.backends.sqlite3' for SQLite.

2. NAME: This indicates the file path where the SQLite database file will be created and stored.

3. By default, it is set to 'db.sqlite3', and it is placed in the project's base directory (BASE_DIR). You can change the name or location of the SQLite database file by modifying this setting.

• When connecting to other databases extra connection parameters will be required, let's take an example of PostgreSQL

    DATABASES = {
      'default': {
          'ENGINE': 'django.db.backends.postgresql',
          'NAME': 'database_name',
          'USER': 'database_user',
          'PASSWORD': 'database_password',
          'HOST': '127.0.0.1',
          'PORT': '5432',
      }
    }
  

Django Migrations

Whenever changes are made to the models in our Django project, we need to execute two commands: makemigrations and migrate.

• makemigrations generates SQL commands for both preinstalled apps and newly created app models that are added to the installed apps.

On the other hand, migrate applies these SQL commands to the database, making the necessary changes.

#create new database migration files
Python manage.py makemigrations

 #this create table in the database
Python manage.py migrate

Crud operation from Admin interface

For this , First I need to register my model in admin.py

from django.contrib import admin
from .models import Post

admin.site.register(Post)

After you register this , then you can do CRUD operation from Django admin interface.

While Django's admin interface provides a user-friendly way to interact with data, the Django shell offers a powerful command-line interface to manage your models and database.

Performing various crud operation from shell

To access the Django shell, open your terminal or command prompt, navigate to your Django project directory, and run the following command:

python manage.py shell

This command open shell terminal where you can perform data operations.

1. Creating Records

    >>>> new_post = Post(
             title = "BitsNotion",  
             description = "Post Description",
             )
    >>> new_post.save()#Save data to database
   

2. Reading Records

   To retrieve record from Post model .We can perform various operations.

   Retrieve all data

    all_posts = Post.objects.all()
   

   Retrieve a specific post by its primary key (id)

    post = Post.objects.get(id=1)
   

   Filter posts based on specific criteria (e.g., title)

    query_set = Post.objects.filter(title='BitsNotion')
   

3. Updating Records

    # Retrieve the post you want to update
    post = Post.objects.get(id=1)
    post.title = 'Updated Post Title'
    post.save()
   

4. Deleting Records

    # Retrieve the post you want to delete
    post = Post.objects.get(id=1)
    post.delete()#delete your post
   

Various model fields list