Gopal Ghate

Posted on Sep 30

🗄️ Django Models & ORM Deep Dive (Article 3)

#django #python #webdev #programming

In the previous article, we set up our first app and rendered a template successfully. Now, it’s time to make our app dynamic by adding a database. Django’s ORM (Object Relational Mapper) allows us to work with databases using Python classes — no SQL required!

In this article, we will cover:

What are models and the Django ORM?
Defining fields and creating migrations.
Performing CRUD operations.
Relationships: One-to-One, One-to-Many, Many-to-Many.
Querying the database.
Quickly testing with sample data.

🏗 What is a Django Model?

A model is a Python class that maps to a database table. Each attribute in the class becomes a column in the table.

Example (blog/models.py):

from django.db import models


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


    def __str__(self):
        return self.title

Django will create a table named blog_post for this model.

🛠 Creating Migrations

Migrations apply model changes to the database:

python manage.py makemigrations
python manage.py migrate

makemigrations → Creates migration files.
migrate → Applies changes to the database.

✍️ CRUD Operations

** Create **

from blog.models import Post

Post.objects.create(title="My First Post", content="This is awesome!")

** Read **

Post.objects.all() # Get all posts
Post.objects.first() # First post
Post.objects.filter(title__icontains="First")

** Update **

post = Post.objects.get(id=1)
post.title = "Updated Title"
post.save()

** Delete **

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

🔗 Relationships Between Models

One-to-Many (ForeignKey)

class Comment(models.Model):
    post = models.ForeignKey(Post, related_name="comments", on_delete=models.CASCADE)
    text = models.TextField()

Each comment belongs to one post.
Access comments: post.comments.all()

One-to-One

from django.contrib.auth.models import User

class AuthorProfile(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    bio = models.TextField()

Many-to-Many

class Tag(models.Model):
    name = models.CharField(max_length=50)
    posts = models.ManyToManyField(Post, related_name="tags")

🔍 Querying the Database

# Exact match
Post.objects.filter(title="My First Post")


# Case-insensitive search
Post.objects.filter(title__icontains="first")


# Order results
Post.objects.order_by('-published_at')


# Access related objects
post = Post.objects.get(id=1)
comments = post.comments.all()

🧪 Testing with Sample Data

You can test models directly in the Django shell:

python manage.py shell # Make sure in the project directory

Inside the shell :

from blog.models import Post

Post.objects.create(title="Sample 1", content="Hello World")
Post.objects.create(title="Sample 2", content="Learning Django ORM")


for post in Post.objects.all():
    print(post.title)

Or load fixtures from a JSON file:

python manage.py loaddata sample_posts.json

🏆 Summary

Models map Python classes to database tables.
Use migrations to apply schema changes.
ORM provides easy CRUD operations.
Relationships (ForeignKey, OneToOne, ManyToMany) connect models.
Querysets allow powerful filtering.
Use Django shell or fixtures to test with sample data.

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