CRUD operations in FastAPI - Mini Project: Build & Apply

CRUD Operations with FastAPI

📖 Scenario: You are building a simple web API to manage a list of books in a library. Each book has an id, title, and author. You will create endpoints to add, read, update, and delete books.

🎯 Goal: Create a FastAPI app with endpoints to perform CRUD (Create, Read, Update, Delete) operations on a list of books stored in memory.

📋 What You'll Learn

Use FastAPI to create the web API

Store books in a list of dictionaries with keys: id, title, author

Create endpoints for: adding a book, getting all books, updating a book by id, and deleting a book by id

Use proper HTTP methods: POST for create, GET for read, PUT for update, DELETE for delete

💡 Why This Matters

🌍 Real World

APIs like this are used to manage data in web applications, mobile apps, and services.

💼 Career

Understanding CRUD operations with FastAPI is essential for backend development roles and building RESTful APIs.

1

Set up initial book data

Create a list called books with these exact entries: {'id': 1, 'title': '1984', 'author': 'George Orwell'} and {'id': 2, 'title': 'Brave New World', 'author': 'Aldous Huxley'}.

FastAPI

# Create the initial list of books
# Your code here

Hint

Use a list with two dictionaries exactly as shown.

2

Create FastAPI app and import

Import FastAPI from fastapi and create an app instance called app.

FastAPI

books = [
    {'id': 1, 'title': '1984', 'author': 'George Orwell'},
    {'id': 2, 'title': 'Brave New World', 'author': 'Aldous Huxley'}
]

# Import FastAPI and create app instance
# Your code here

Hint

Use from fastapi import FastAPI and then app = FastAPI().

3

Add GET endpoint to read all books

Create a GET endpoint at /books using @app.get('/books') that returns the books list.

FastAPI

from fastapi import FastAPI

books = [
    {'id': 1, 'title': '1984', 'author': 'George Orwell'},
    {'id': 2, 'title': 'Brave New World', 'author': 'Aldous Huxley'}
]

app = FastAPI()

# Create GET endpoint to return all books
# Your code here

Hint

Use @app.get('/books') decorator and a function that returns books.

4

Add POST, PUT, DELETE endpoints for CRUD

Add these endpoints to app: - POST /books to add a new book from JSON body - PUT /books/{book_id} to update a book's title and author by book_id - DELETE /books/{book_id} to remove a book by book_id Use @app.post, @app.put, and @app.delete decorators respectively.

FastAPI

from fastapi import FastAPI
from fastapi import Request

books = [
    {'id': 1, 'title': '1984', 'author': 'George Orwell'},
    {'id': 2, 'title': 'Brave New World', 'author': 'Aldous Huxley'}
]

app = FastAPI()

@app.get('/books')
def get_books():
    return books

# Add POST, PUT, DELETE endpoints below
# Your code here

Hint

Use async functions with appropriate decorators and handle book list updates. Raise 404 error if book not found.

Practice

1. What does CRUD stand for in FastAPI applications?

easy

A. Cache, Route, Undo, Debug

B. Create, Read, Update, Delete

C. Compile, Render, Use, Deploy

D. Connect, Run, Upload, Download

Solution

1. Step 1: Understand CRUD basics

   CRUD is a common acronym in web development representing the four basic operations on data.

2. Step 2: Match CRUD to FastAPI operations

   FastAPI supports these operations: creating, reading, updating, and deleting data.

3. Final Answer:

   Create, Read, Update, Delete -> Option B

4. Quick Check:

   CRUD = Create, Read, Update, Delete [OK]

Hint: Remember CRUD as the four main data actions [OK]

Common Mistakes:

• Confusing CRUD with unrelated terms
• Thinking CRUD includes deployment steps
• Mixing CRUD with HTTP methods only

2. Which FastAPI decorator is used to define a route for updating an existing item?

easy

A. @app.put()

B. @app.get()

C. @app.post()

D. @app.delete()

Solution

1. Step 1: Identify HTTP methods for CRUD

   Update operations typically use the HTTP PUT method.

2. Step 2: Match HTTP method to FastAPI decorator

   FastAPI uses @app.put() to define routes that update existing data.

3. Final Answer:

   @app.put() -> Option A

4. Quick Check:

   Update = @app.put() [OK]

Hint: Update uses PUT method and @app.put() decorator [OK]

Common Mistakes:

• Using @app.post() for update routes
• Confusing @app.get() with update
• Using @app.delete() instead of update

3. Given this FastAPI code snippet, what will be the response when accessing GET /items/42 if the item exists?

from fastapi import FastAPI
app = FastAPI()
items = {42: {"name": "Book", "price": 10.99}}

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    return items.get(item_id, {"error": "Item not found"})

medium

A. 404 Not Found error

B. {"error": "Item not found"}

C. {"name": "Book", "price": 10.99}

D. Empty response

Solution

1. Step 1: Understand the dictionary lookup

   The code uses items.get(item_id, {"error": "Item not found"}) which returns the item if found, else an error dict.

2. Step 2: Check if item 42 exists

   Item 42 is in the dictionary with name "Book" and price 10.99, so it will be returned.

3. Final Answer:

   {"name": "Book", "price": 10.99} -> Option C

4. Quick Check:

   Item found returns data, else error [OK]

Hint: dict.get returns value if key exists, else default [OK]

Common Mistakes:

• Assuming a 404 error is raised automatically
• Expecting an empty response if item exists
• Confusing error message with actual data

4. Identify the error in this FastAPI DELETE route code:

from fastapi import FastAPI
app = FastAPI()
items = {1: "apple", 2: "banana"}

@app.delete("/items/{item_id}")
async def delete_item(item_id: int):
    del items[item_id]
    return {"message": "Item deleted"}

medium

A. Incorrect route path syntax

B. Missing return type annotation

C. Using async def instead of def

D. Deleting item without checking if it exists

Solution

1. Step 1: Analyze deletion logic

   The code deletes the item directly without checking if the item_id exists in the dictionary.

2. Step 2: Understand potential error

   If item_id is not in items, del will raise a KeyError causing a server error.

3. Final Answer:

   Deleting item without checking if it exists -> Option D

4. Quick Check:

   Always check existence before deleting [OK]

Hint: Check key exists before deleting to avoid errors [OK]

Common Mistakes:

• Ignoring KeyError on missing keys
• Thinking async def causes error here
• Assuming route path syntax is wrong

5. You want to create a FastAPI endpoint to update an item only if it exists, otherwise return a 404 error. Which code snippet correctly implements this behavior? A:

@app.put("/items/{item_id}")
async def update_item(item_id: int, item: dict):
    items[item_id] = item
    return item

B:

@app.put("/items/{item_id}")
async def update_item(item_id: int, item: dict):
    if item_id not in items:
        return {"error": "Not found"}
    items[item_id] = item
    return item

C:

from fastapi import HTTPException
@app.put("/items/{item_id}")
async def update_item(item_id: int, item: dict):
    if item_id not in items:
        raise HTTPException(status_code=404, detail="Item not found")
    items[item_id] = item
    return item

D:

@app.put("/items/{item_id}")
async def update_item(item_id: int, item: dict):
    try:
        items[item_id] = item
    except KeyError:
        return {"error": "Not found"}
    return item

hard

A. Raises HTTPException with 404 status if missing

B. Returns error dict but no HTTP status code change

C. Updates without checking existence, no error if missing

D. Catches KeyError incorrectly, since assignment won't raise it

Solution

1. Step 1: Understand proper 404 error handling in FastAPI

   FastAPI uses HTTPException to return HTTP errors with status codes.

2. Step 2: Analyze each option's error handling

   The snippet using HTTPException(status_code=404, detail="Item not found") correctly returns a 404 response. Others either update without checking (200 OK), return an error dict as 200 OK, or misuse try-except since assignment does not raise KeyError.

3. Final Answer:

   Raises HTTPException with 404 status if missing -> Option A

4. Quick Check:

   Use HTTPException for proper HTTP error responses [OK]

Hint: Use HTTPException to return 404 errors in FastAPI [OK]

Common Mistakes:

• Returning error dict without HTTP status change
• Assuming assignment raises KeyError
• Not raising HTTPException for errors