Service layer pattern in Flask - Mini Project: Build & Apply

Building a Service Layer in Flask

📖 Scenario: You are creating a simple Flask web app to manage a list of books. You want to keep your code clean by separating the logic that handles book data from the web routes. This is done using a service layer.

🎯 Goal: Build a Flask app with a service layer that manages book data separately from the route handlers.

📋 What You'll Learn

Create a list of books as initial data

Add a configuration variable for minimum title length

Implement a service class with a method to get books with titles longer than the minimum length

Use the service class in a Flask route to display filtered books

💡 Why This Matters

🌍 Real World

Service layers help keep web apps organized by separating business logic from web routes, making code easier to maintain and test.

💼 Career

Understanding service layers is important for backend developers working with Flask or similar frameworks to build clean, scalable applications.

1

DATA SETUP: Create the initial book list

Create a list called books with these exact dictionaries: {'id': 1, 'title': 'Flask Basics'}, {'id': 2, 'title': 'Advanced Flask'}, and {'id': 3, 'title': 'Python Tips'}.

Flask

# Create the list of books
# Your code here

Need a hint?

Use a list with dictionaries inside. Each dictionary has keys 'id' and 'title'.

2

CONFIGURATION: Add minimum title length variable

Create a variable called MIN_TITLE_LENGTH and set it to 12.

Flask

books = [
    {'id': 1, 'title': 'Flask Basics'},
    {'id': 2, 'title': 'Advanced Flask'},
    {'id': 3, 'title': 'Python Tips'}
]
# Define minimum title length
# Your code here

Need a hint?

Just create a variable with the exact name and value.

3

CORE LOGIC: Implement the BookService class

Create a class called BookService with an __init__ method that takes books and min_length. Add a method called get_long_titles that returns a list of books with titles longer than min_length. Use a list comprehension with book['title'] and min_length.

Flask

books = [
    {'id': 1, 'title': 'Flask Basics'},
    {'id': 2, 'title': 'Advanced Flask'},
    {'id': 3, 'title': 'Python Tips'}
]

MIN_TITLE_LENGTH = 12

# Create BookService class with __init__ and get_long_titles method
# Your code here

Need a hint?

Use a class with an __init__ method to save books and min_length. Use a list comprehension in get_long_titles.

4

COMPLETION: Use BookService in a Flask route

Import Flask and create an app with app = Flask(__name__). Create a route @app.route('/books') with a function show_books. Inside it, create a BookService instance with books and MIN_TITLE_LENGTH. Return a string joining the titles from get_long_titles() separated by commas.

Flask

books = [
    {'id': 1, 'title': 'Flask Basics'},
    {'id': 2, 'title': 'Advanced Flask'},
    {'id': 3, 'title': 'Python Tips'}
]

MIN_TITLE_LENGTH = 12

class BookService:
    def __init__(self, books, min_length):
        self.books = books
        self.min_length = min_length

    def get_long_titles(self):
        return [book for book in self.books if len(book['title']) > self.min_length]

# Import Flask and create app
# Add route /books that uses BookService to return titles
# Your code here

Need a hint?

Import Flask, create app, define route, create service instance, get filtered books, join titles, and return string.