Table 1: authors

Structure (columns)

Column name	Type	Constraints
id	BIGSERIAL	Primary Key
name	VARCHAR(200)	NOT NULL
email	VARCHAR(254)	UNIQUE, NOT NULL
is_active	BOOLEAN	DEFAULT TRUE
created_at	TIMESTAMPTZ	DEFAULT NOW()

Sample data in authors

id	name	email	is_active	created_at
1	George Orwell	orwell@example.com	true	2026-01-21 10:15:00
2	Rowling	rowling@example.com	true	2026-01-21 10:20:00
3	Inactive Author	inactive@example.com	false	2026-01-21 10:30:00

---

Table 2: books

Structure (columns)

Column name	Type	Constraints
id	BIGSERIAL	Primary Key
author_id	BIGINT	FK → authors(id), NOT NULL
title	VARCHAR(200)	NOT NULL
published_year	SMALLINT	NOT NULL
price	NUMERIC(8,2)	NOT NULL
is_published	BOOLEAN	DEFAULT TRUE
UNIQUE	(author_id, title)	One title per author

Sample data in books

id	author_id	title	published_year	price	is_published
1	1	1984	1949	9.99	true
2	1	Animal Farm	1945	7.99	true
3	2	Harry Potter	1997	19.99	true
4	2	The Casual Vacancy	2012	14.50	true

---

Relationship explained visually

authors
+----+-----------------+
| id | name            |
+----+-----------------+
| 1  | George Orwell   |
| 2  | J. K. Rowling   |
+----+-----------------+
        ↑
        │ author_id
        │
books
+----+-----------+--------------------+
| id | author_id | title              |
+----+-----------+--------------------+
| 1  | 1         | 1984               |
| 2  | 1         | Animal Farm        |
| 3  | 2         | Harry Potter       |
| 4  | 2         | The Casual Vacancy |
+----+-----------+--------------------+

---

Relationship summary

authors
-------
id (PK)
name
email (UNIQUE)
is_active
created_at

        1
        |
        |
        |
        *
books
-----
id (PK)
author_id (FK → authors.id)
title
published_year
price
is_published

• One Author → Many Books

• Foreign key lives in books

• Reverse access via:

author.books.all()

---

How Django ORM sees this

Forward (Book → Author)

book.author

Reverse (Author → Book)

author.books.all()

---

How to see this yourself

Run:

python manage.py sqlmigrate myapp 0001

You’ll see SQL very close to what I showed.

Or in PostgreSQL:

• d authors

• d books

Key takeaways

models.py → defines tables
ForeignKey → creates *_id column
unique=True → UNIQUE constraint
Index → CREATE INDEX
validators → Python-level (not DB-level)

---

Open:

myapp/models.py

Put exactly this:

from django.db import models
from django.core.validators import MinValueValidator

class Author(models.Model):
    name = models.CharField(max_length=200)
    email = models.EmailField(unique=True)
    is_active = models.BooleanField(default=True)
    created_at = models.DateTimeField(auto_now_add=True)

    class Meta:
        db_table = "authors"
        indexes = [
            models.Index(fields=["email"]),
        ]

    def __str__(self):
        return self.name


class Book(models.Model):
    author = models.ForeignKey(
        Author,
        on_delete=models.CASCADE,
        related_name="books",
    )
    title = models.CharField(max_length=200)
    published_year = models.PositiveSmallIntegerField(
        validators=[MinValueValidator(1)]
    )
    price = models.DecimalField(
        max_digits=8,
        decimal_places=2
    )
    is_published = models.BooleanField(default=True)

    class Meta:
        db_table = "books"
        constraints = [
            models.UniqueConstraint(
                fields=["author", "title"],
                name="uniq_book_per_author",
            )
        ]
        indexes = [
            models.Index(fields=["author"]),
            models.Index(fields=["published_year"]),
        ]

    def __str__(self):
        return self.title