Add a new field

📅 Adding a Published Date Field to the Book API

In this phase, we will enhance our API by introducing a new field:

👉 published_date

This field will allow us to:

Store the year a book was published
Validate that the year is within an acceptable range
Filter books based on publication year

We will represent published_date as an integer year, for example:

This keeps the system simple while still demonstrating important backend validation concepts.

🧱 Step 1: Update the `Book` Domain Model

First, we must update our internal domain object.

Remember:

Book → Internal business object
BookRequest → API boundary model (Pydantic)

👉 We begin by adding published_date to the Book class.

class Book:
    id: int
    title: str
    author: str
    description: str
    rating: int
    published_date: int

    def __init__(self, id, title, author, description, rating, published_date):
        self.id = id
        self.title = title
        self.author = author
        self.description = description
        self.rating = rating
        self.published_date = published_date

🔎 What Changed?

Added published_date: int
Updated the constructor to accept published_date
Every Book object must now include this field

👉 This ensures consistency across our backend system.

🧪 Step 2: Add Validation to `BookRequest`

Now we update the Pydantic request model.

This is where validation happens before business logic runs.

We will enforce:

Year must be greater than 1999
Year must be less than 2031

class BookRequest(BaseModel):
    id: Optional[int] = Field(description="ID is not required", default=None)
    title: str = Field(min_length=3)
    author: str = Field(min_length=1)
    description: str = Field(min_length=1, max_length=100)
    rating: int = Field(gt=1, lt=6)
    published_date: int = Field(gt=1999, lt=2031)

🧠 Why Validate Here?

Because:

Validation belongs at the API boundary
Bad data should never enter your system
FastAPI + Pydantic reject invalid input automatically

If a user submits:

FastAPI will return:

HTTP 422 — Unprocessable Entity

👉 And your function will never execute.

🧭 Step 3: Improve Swagger Documentation with an Example

Now let’s guide API users properly.

We’ll add published_date to the schema example.

class BookRequest(BaseModel):
    id: Optional[int] = Field(description="ID is not required", default=None)
    title: str = Field(min_length=3)
    author: str = Field(min_length=1)
    description: str = Field(min_length=1, max_length=100)
    rating: int = Field(gt=1, lt=6)
    published_date: int = Field(gt=1999, lt=2031)

    model_config = {
        "json_schema_extra": {
            "example": {
                "title": "A new book",
                "author": "Name of the author",
                "description": "The description of the book",
                "rating": 5,
                "published_date": 2029
            }
        }
    }

🔎 What This Does

In Swagger UI:

published_date appears in the schema
A full example payload is displayed
Users understand exactly how to structure their request

👉 This improves developer experience significantly.

📚 Step 4: Update the Sample Data

Now update the in-memory BOOKS list.

BOOKS = [
 Book(1, "Computer Science Pro", "codingwithrobby", "A very nice book", 3, 2030),
 Book(2, "Be Fast with FastAPI", "codingwithrobby", "A great book", 5, 2030),
 Book(3, "Master Endpoints", "codingwithrobby", "An awesome book", 5, 2029),
 Book(4, "HP1", "Author 1", "Book Description", 2, 2028),
 Book(5, "HP2", "Author 2", "Book Description", 3, 2027),
 Book(6, "HP3", "Author 3", "Book Description", 1, 2026)
]

🧠 Backend Insight

Now your system supports:

Storage of publication year
Filtering by year
Validation before insertion
Consistent domain modeling

You are gradually building a properly structured backend.

🔍 Step 5: Create an Endpoint to Filter by Published Date

We will now create a GET endpoint that filters by publication year.

@app.get("/books/publish/")
async def read_books_by_publish_date(published_date: int): # 👉 Query parameter
    books_to_return = []
    for book in BOOKS:
        if book.published_date == published_date:
            books_to_return.append(book)
    return books_to_return

🔎 What Is Happening Here?

published_date is a query parameter
FastAPI extracts and validates it as int
We loop through the books
We return only matching years

Example request:

GET /books/publish/?published_date=2030

🌐 Step 6: Test in the Browser

👉 Open Swagger UI

Try the following:

Search using a valid year (e.g., 2029)
Create a book with 2025
Try invalid years like:
- 1990
- 2050

You should receive:

HTTP 422 — Unprocessable Entity

👉 This confirms validation is working correctly.

🗂️ books2.py

from typing import Optional
from fastapi import FastAPI
from pydantic import BaseModel, Field

app = FastAPI()

class Book:
    id: int
    title: str
    author: str
    description: str
    rating: int
    published_date: int

    def __init__(self, id, title, author, description, rating, published_date):
        self.id = id
        self.title = title
        self.author = author
        self.description = description
        self.rating = rating
        self.published_date = published_date

class BookRequest(BaseModel):
    id: Optional[int] = Field(description="ID is not required", default=None)
    title: str = Field(min_length=3)
    author: str = Field(min_length=1)
    description: str = Field(min_length=1, max_length=100)
    rating: int = Field(gt=1, lt=6)
    published_date: int = Field(gt=1999, lt=2031)

    model_config = {
        "json_schema_extra": {
            "example": {
                "title": "A new book",
                "author": "Name of the author",
                "description": "The description of the book",
                "rating": 5,
                "published_date": 2029
            }
        }
    }

BOOKS = [
    Book(1, "Computer Science Pro", "codingwithrobby", "A very nice book", 3, 2030),
    Book(2, "Be Fast with FastAPI", "codingwithrobby", "A great book", 5, 2030),
    Book(3, "Master Endpoints", "codingwithrobby", "An awesome book", 5, 2029),
    Book(4, "HP1", "Author 1", "Book Description", 2, 2028),
    Book(5, "HP2", "Author 2", "Book Description", 3, 2027),
    Book(6, "HP3", "Author 3", "Book Description", 1, 2026)
]

@app.get("/books")
async def read_all_books():
    return BOOKS

@app.post("/create_book")
async def create_book(book_request: BookRequest):
    new_book = Book(**book_request.model_dump())
    BOOKS.append(find_book_id(new_book))
    
@app.get("/books/{book_id}") 
async def read_book(book_id: int):
    for book in BOOKS:
        if book.id == book_id:
            return book

@app.get("/books/")
async def read_book_by_rating(book_rating: int):
    books_to_return = []
    for book in BOOKS:
        if book.rating == book_rating:
            books_to_return.append(book)
    return books_to_return
    
@app.put("/books/update_book")
async def update_book(book: BookRequest):
    for i in range(len(BOOKS)):
        if BOOKS[i].id == book.id:
            BOOKS[i] = book
            
@app.delete("/books/{book_id}")
async def delete_book(book_id: int):
    for i in range(len(BOOKS)):
        if BOOKS[i].id == book_id:
            BOOKS.pop(i)
            break
            
@app.get("/books/publish/")
async def read_books_by_publish_date(published_date: int):
    books_to_return = []
    for book in BOOKS:
        if book.published_date == published_date:
            books_to_return.append(book)
    return books_to_return
    
def find_book_id(book: Book):
    book.id = 1 if len(BOOKS) == 0 else BOOKS[-1].id + 1
    return book