Django Models and Migrations

Django’s ORM (Object-Relational Mapping) allows developers to interact with databases using Python code instead of raw SQL. Models define the structure of your database tables, while migrations help apply changes to the database.

In this tutorial, we will cover:

• What are Django models?
• Defining models in Django
• Running migrations to create database tables
• Working with models in the Django shell

1. What are Django Models?

A model in Django is a Python class that represents a database table. Each attribute in the model corresponds to a column in the database. Django provides built-in fields like CharField, IntegerField, and DateTimeField to define data types.

2. Creating a Django Model

To define a model, open the models.py file inside your Django app and add the following code:

from django.db import models

class Student(models.Model):
    name = models.CharField(max_length=100)
    age = models.IntegerField()
    email = models.EmailField(unique=True)
    enrollment_date = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return self.name

Explanation:

• name: A text field with a maximum length of 100 characters.
• age: An integer field.
• email: An email field that must be unique.
• enrollment_date: Stores the date and time when the student was added.
• __str__(): Returns the student’s name when printed.

3. Applying Migrations

Once the model is defined, we need to create and apply database migrations.

Step 1: Create Migration

Run the following command to generate a migration file:

python manage.py makemigrations

Django will create a migration file inside the migrations directory of your app.

Step 2: Apply Migration

Apply the changes to the database:

python manage.py migrate

This creates the corresponding table in the database.

4. Registering Models in Admin Panel

To manage models in the Django admin panel, register them in admin.py:

from django.contrib import admin
from .models import Student

admin.site.register(Student)

Now, run the server and visit http://127.0.0.1:8000/admin/. You will be able to see and manage students in the Django admin panel.

5. Working with Models in Django Shell

Django provides an interactive shell to interact with the database.

Run the shell:

python manage.py shell

Then, execute the following commands:

from myapp.models import Student

# Creating a new student
student = Student(name="Amit Sharma", age=22, email="amit@example.com")
student.save()

# Fetching all students
students = Student.objects.all()
print(students)

# Filtering students
young_students = Student.objects.filter(age__lt=25)
print(young_students)

6. Common Model Operations

Updating a Record

student = Student.objects.get(id=1)
student.name = "Rahul Verma"
student.save()

Deleting a Record

student = Student.objects.get(id=1)
student.delete()

Conclusion

Django models provide a powerful way to define database structures using Python code. With migrations, you can easily apply changes to your database without manually writing SQL queries.