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Object-Relational Mapping

Learn more about Object-Relational Mapping and RAW Selects in Django (Intro for Beginners).

Django's Object-Relational Mapping (ORM) is a powerful tool that allows you to interact with your database using Python code, without writing SQL queries directly.

It abstracts the database and provides a high-level, Pythonic way of managing and querying data.

Object-Relational Mapping and RAW Selects in Django - Tutorial provided by AppSeed.

Here's a comprehensive introduction to Django ORM, along with samples and a brief introduction to raw SQL selects.

✅ Setting up Models​

In Django, models represent your application's data structure. They are defined in Python and automatically generate the database schema. Here's an example of defining a simple model:

from django.db import models

class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)
    publication_date = models.DateField()

✅ Creating Tables​

After defining your models, you need to create database tables. Run the following command:

python manage.py makemigrations
python manage.py migrate

This will create the necessary tables in your database.

✅ Querying with Django ORM​

Django ORM provides a rich API for querying the database. Here are some common queries:

Filtering

# Retrieve all books with 'Django' in the title
books = Book.objects.filter(title__icontains='Django')

Joins

# Retrieve books with their author's name
books_with_author = Book.objects.select_related('author')

Aggregation

from django.db.models import Count
# Count the number of books by each author
author_book_count = Author.objects.annotate(num_books=Count('book'))

Sorting

# Sort books by publication date in descending order
books = Book.objects.order_by('-publication_date')

Inserting Data

new_author = Author.objects.create(name='J.K. Rowling')
new_book = Book.objects.create(title='Harry Potter', author=new_author, publication_date='1997-06-26')

Updating Data

book = Book.objects.get(title='Harry Potter')
book.title = 'Harry Potter and the Philosopher\'s Stone'
book.save()

Deleting Data

book = Book.objects.get(title='Harry Potter')
book.delete()

✅ Using Raw SQL Queries​

While Django ORM is excellent for most tasks, there may be cases where you need to execute raw SQL queries. You can use the connection object for this purpose. For example:

from django.db import connection

def custom_sql_query():
    with connection.cursor() as cursor:
        cursor.execute("SELECT * FROM myapp_book WHERE title = %s", ['Harry Potter'])
        results = cursor.fetchall()
    return results

Remember to use raw SQL sparingly, as it bypasses Django's security features and may make your code less portable.

✅ In Summary​

These are the basics of Django ORM and using raw SQL queries in Django. It's a powerful tool that can make database interactions in your web application more manageable and Pythonic.

✅ Resources​