Interview question

What is Django's ORM and what problem does it solve? Django का ORM क्या है और यह कौन-सी problem solve करता है?

Answer

Django's ORM (Object-Relational Mapper) lets developers interact with the database using Python classes and methods instead of writing raw SQL, mapping Python objects to database tables automatically.

# models.py - defining a model maps directly to a database table
from django.db import models

class Author(models.Model):
    name = models.CharField(max_length=100)
    email = models.EmailField(unique=True)

class Book(models.Model):
    title = models.CharField(max_length=200)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)
    published_date = models.DateField()
    price = models.DecimalField(max_digits=6, decimal_places=2)

# Using the ORM - no raw SQL needed
book = Book.objects.create(
    title='Django for Beginners',
    author=Author.objects.create(name='John', email='john@example.com'),
    published_date='2024-01-01',
    price=29.99
)

# Equivalent raw SQL the ORM generates behind the scenes (roughly):
# INSERT INTO myapp_book (title, author_id, published_date, price)
# VALUES ('Django for Beginners', 1, '2024-01-01', 29.99);

books = Book.objects.filter(price__lt=50)
for b in books:
    print(b.title, b.author.name)

Benefit	Explanation
Database portability	Same Python code works across PostgreSQL, MySQL, SQLite, etc.
SQL injection protection	ORM automatically parameterizes queries
Migrations	Schema changes tracked and versioned as Python code

Django का ORM (Object-Relational Mapper) developers को raw SQL लिखने की बजाय Python classes और methods से database से interact करने देता है, Python objects को automatically database tables से map करता है।

# models.py
from django.db import models

class Author(models.Model):
    name = models.CharField(max_length=100)
    email = models.EmailField(unique=True)

class Book(models.Model):
    title = models.CharField(max_length=200)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)
    published_date = models.DateField()
    price = models.DecimalField(max_digits=6, decimal_places=2)

# ORM use करना - raw SQL नहीं चाहिए
book = Book.objects.create(
    title='Django for Beginners',
    author=Author.objects.create(name='John', email='john@example.com'),
    published_date='2024-01-01',
    price=29.99
)

books = Book.objects.filter(price__lt=50)
for b in books:
    print(b.title, b.author.name)

फायदा	विवरण
Database portability	PostgreSQL, MySQL, SQLite में same code चलता है
SQL injection protection	ORM automatically queries parameterize करता है
Migrations	Schema changes tracked और versioned

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