Design Patterns for developers
In software development, design patterns are reusable solutions to common problems that developers encounter. These patterns provide a structure for organizing code that makes it more maintainable, modular, and scalable.
In modern backend development, design patterns are crucial for building robust and flexible systems that can adapt to changing requirements and user needs.
In this tutorial, we will explore the most common design patterns used in modern backend development. We’ll also see how to apply them in real-world scenarios.
Design patterns are proven solutions to commonly occurring problems in software development. They are not specific to any particular programming language or platform but can be applied to any software system.
In this tutorial, I will be using TypeScript to illustrate the common patterns covered here.
What we’ll cover:
- Importance of Design Patterns in Software Development
- A Brief Overview of Modern Backend Development
- Advantages of Using Design Patterns in Backend Development
- Common Design Patterns for Modern Backend Development
– MVC (Model-View-Controller) Pattern
– Repository Pattern
– Dependency Injection Pattern
– Observer Pattern
– Decorator Pattern - Real-world Examples of Design Patterns in Backend Development
– MVC Pattern in a Web App
– Repository Pattern with a Database
– Dependency Injection Pattern for Decoupling Dependencies
– Observer Pattern for Event Driven Programming
– Decorator Pattern for Adding Functionality to a Class Dynamically - Conclusion
- Next Steps
Importance of Design Patterns in Software Development
Design patterns offer numerous advantages in software development. They can simplify the coding process, enhance code maintainability, and promote code reuse.
They also help developers write code that is more efficient, scalable, and adaptable. And they’re incredibly beneficial when working on a project with multiple contributors. This is because design patterns provide a shared framework of best practices that can ensure consistency across the codebase.
A Brief Overview of Modern Backend Development
Modern backend development is all about creating software systems that power the server-side of web applications and services.
To achieve this, backend developers need to design systems that are scalable, reliable, and efficient. This often involves using cloud-based technologies and microservices architecture, which enables developers to build systems that can handle high traffic loads, while also being flexible and easily manageable.
In addition to the use of modern technologies, design patterns play a crucial role in building robust and maintainable systems. By using established design patterns, developers can create modular, maintainable, and extendable systems that are easier to manage and improve over time.
Overall, modern backend development requires a deep understanding of software architecture, cloud-based technologies, and design patterns. By leveraging these tools and techniques, backend developers can create systems that are scalable, reliable, efficient, and easy to maintain over time.
Advantages of Using Design Patterns in Backend Development
Design patterns are tried and tested solutions to common problems that developers encounter in software development. They provide a structured approach to solving these problems, making it easier for developers to write maintainable, scalable, and reusable code.
In this section, we will discuss the advantages of using design patterns in backend development.
- Code reusability: One of the main advantages of using design patterns is code reusability. By following a standard structure, developers can easily reuse code in different parts of an application or even in different applications altogether.
- Scalability: Design patterns allow for scalability in applications, as they provide a structured approach to writing code. This makes it easier to add new features or make changes to existing ones without disrupting the overall architecture of the application.
- Maintainability: Using design patterns can make code more maintainable, as they provide a standardized approach to solving problems. This makes it easier for developers to understand code written by others and to maintain it over time.
- Reduced errors: Design patterns are tried and tested solutions to common problems. By using these patterns, developers can avoid common errors and pitfalls that might arise when writing code from scratch.
- Performance: Design patterns can improve the performance of an application by providing a structured approach to solving problems. This can result in more efficient code that executes faster and uses fewer resources.
Common Design Patterns for Modern Backend Development
In modern backend development, there are several design patterns that are widely used to build scalable, maintainable, and efficient systems.
In this section, we will discuss some of the most commonly used design patterns in modern backend development.
MVC (Model-View-Controller) Pattern
The Model-View-Controller (MVC) pattern is a widely used design pattern in modern backend development. It provides a way to separate the presentation layer (the View) from the business logic and data storage layers (the Model and Controller). This separation allows developers to write more modular and maintainable code.
In the MVC pattern, the Model represents the data and business logic of the application. The Controller acts as an intermediary between the Model and the View, handling user input and updating the Model accordingly. The View is responsible for presenting data to the user and receiving user input.
One of the main advantages of using the MVC pattern is that it allows for easy testing and maintenance of the codebase. Since the Model and Controller are separate from the View, it is possible to test and modify each component independently.
Another benefit of using the MVC pattern is that it lets you reuse code. The Model and Controller can be reused in different Views, providing a more modular approach to software development.
Overall, the MVC pattern is a useful tool for creating scalable, maintainable, and efficient backend systems. It separates concerns and enables a more modular approach to software development, making it easier to test, maintain, and modify the codebase.
Repository Pattern
The Repository Pattern is a design pattern that provides an abstraction layer between the data access layer and the rest of the application. It separates the logic that retrieves data from the data storage layer, providing a more modular approach to software development.
In the Repository Pattern, a repository acts as a mediator between the data storage layer and the application logic layer. It provides a single point of entry for retrieving and manipulating data, allowing the rest of the application to be decoupled from the specifics of the data storage layer. This makes it easier to change the data storage layer without affecting the rest of the application.
One of the main advantages of using the Repository Pattern is that it enables a more modular approach to software development. The application logic layer is separated from the data storage layer, making it easier to test and maintain each component separately. This also makes it possible to reuse the application logic layer with different data storage layers.
Another benefit of using the Repository Pattern is that it can improve performance by reducing the number of calls to the data storage layer. Since the data access logic is encapsulated within the repository, it is possible to optimize queries and reduce the number of database calls.
Overall, the Repository Pattern is a useful tool for creating scalable, maintainable, and efficient backend systems. It separates concerns and enables a more modular approach to software development, making it easier to test, maintain, and modify the codebase. It can also improve performance by reducing the number of calls to the data storage layer.
Dependency Injection Pattern
The Dependency Injection (DI) Pattern is a design pattern that enables the creation of loosely coupled software components. It is used to reduce the coupling between components and improve the flexibility, testability, and maintainability of the code.
In the Dependency Injection Pattern, dependencies are injected into a component rather than being created within the component. This allows components to be created independently of their dependencies, making it easier to replace or modify dependencies without affecting the component itself.
There are three main types of Dependency Injection: Constructor Injection, Property Injection, and Method Injection.
Constructor Injection involves passing dependencies to a component through its constructor. Property Injection involves setting dependencies through public properties of the component. Method Injection involves passing dependencies to methods of the component.
One of the main advantages of using the Dependency Injection Pattern is that it improves the testability of the code. By injecting dependencies into a component, it is possible to create unit tests that isolate the component from its dependencies, making it easier to test the component in isolation.
Another benefit of using the Dependency Injection Pattern is that it makes the code more flexible and maintainable. By reducing the coupling between components, it is easier to modify or replace components without affecting the rest of the application.
Overall, the Dependency Injection Pattern is a useful tool for creating scalable, maintainable, and efficient backend systems. It reduces the coupling between components and improves the flexibility, testability, and maintainability of the code.
Observer Pattern
The Observer Pattern is a design pattern that allows an object (the subject) to notify other objects (the observers) when its state changes. It provides a way for objects to communicate with each other without having direct knowledge of each other’s existence.
In the Observer Pattern, the subject maintains a list of observers and notifies them when its state changes. The observers can then take action based on the change in the subject’s state. This allows for a loosely coupled relationship between the subject and observers, making it easier to modify or extend the system.
One of the main advantages of using the Observer Pattern is that it improves the modularity and flexibility of the code. By separating the subject and observers, it is possible to add or remove observers without affecting the subject, or add new subjects without affecting the existing observers.
Another benefit of using the Observer Pattern is that it can improve the performance of the system. By notifying only the observers that are interested in the change, it is possible to reduce the number of notifications and improve the overall performance of the system.
Overall, the Observer Pattern is a useful tool for creating scalable, maintainable, and efficient backend systems. It allows for a loosely coupled relationship between objects, improving the modularity and flexibility of the code. It can also improve the performance of the system by reducing the number of notifications.
Decorator Pattern
The Decorator Pattern is a design pattern that allows behavior to be added to an individual object, either statically or dynamically, without affecting the behavior of other objects from the same class. It is used to add functionality to objects at runtime, instead of at compile time.
In the Decorator Pattern, a decorator class is used to wrap the original object. The decorator class has the same interface as the original object, allowing it to be used in the same way. The decorator class then adds behavior to the original object by delegating some of its work to the wrapped object and adding its own behavior.
One of the main advantages of using the Decorator Pattern is that it allows for the dynamic addition of functionality to objects. This can be useful in situations where the behavior of an object needs to be changed at runtime, or where the behavior of an object needs to be extended without changing its interface.
Another benefit of using the Decorator Pattern is that it can improve the maintainability of the code. Since the behavior of the object is separated into individual decorators, it is easier to modify or extend the behavior of the object without affecting other parts of the system.
Overall, the Decorator Pattern is a useful tool for creating scalable, maintainable, and efficient backend systems. It allows for the dynamic addition of functionality to objects, improving the flexibility and maintainability of the code.
Real-world Examples of Design Patterns in Backend Development
In this section, we’ll explore some real-world examples of how design patterns can be used in backend development.
Design patterns are a powerful tool that can help developers create scalable, maintainable, and efficient systems. By using design patterns, developers can reuse existing solutions to common problems, reducing development time and improving the quality of the code.
In this section, we’ll look at some examples of how design patterns are used in popular backend frameworks, including Express.js and Django. We’ll explore how these frameworks use design patterns to solve common problems, and how developers can apply these patterns in their own projects.
So, let’s dive in and explore some real-world examples of design patterns in backend development.
Example of using the MVC pattern in a web application
First, we’ll look at an example of using the MVC pattern in a web application with the popular Node.js framework, Express.js.
In an Express.js application, the Model component is often implemented using a database such as MongoDB or MySQL. The View component is usually implemented using templating engines such as EJS or Handlebars. The Controller component is implemented using middleware functions, which are functions that are executed in a specific order when a request is made to the server.
For example, when a user makes a request to view a blog post, the request is handled by the Controller component. The Controller retrieves the blog post from the Model component and passes it to the View component, which renders it using a templating engine. The resulting HTML is then sent back to the user’s browser.
Using the MVC pattern in a web application can provide a number of benefits, including improved scalability, maintainability, and testability. By separating the application into distinct components, developers can make changes to one component without affecting the others. This can make it easier to maintain and test the application over time.
In the following example, the Model is represented by the PostModel class, which is responsible for fetching and saving data to a database.
The View is represented by the PostView class, which is responsible for rendering the HTML page and handling user input.
The Controller is represented by the PostController class, which acts as an intermediary between the Model and View. It initializes the View, handles user input, and updates the View based on changes to the Model.
// the model
interface Post {
id: number;
title: string;
content: string;
date: Date;
}
class PostModel {
private posts: Post[] = [];
getPosts() {
// fetch posts from database
return this.posts;
}
addPost(post: Post) {
// save post to database
this.posts.push(post);
}
}
// the view
class PostView {
displayPosts(posts: Post[]) {
// render posts to the HTML page
}
getPostFromInput(): Post {
// retrieve input values from the HTML page
// and create a new Post object
}
}
// the controller
class PostController {
private model: PostModel;
private view: PostView;
constructor(model: PostModel, view: PostView) {
this.model = model;
this.view = view;
}
init() {
// initialize the view
this.view.displayPosts(this.model.getPosts());
}
addPost() {
// get new post from view
const post = this.view.getPostFromInput();
// add post to model
this.model.addPost(post);
// update view
this.view.displayPosts(this.model.getPosts());
}
}
This implementation of the MVC pattern allows for separation of concerns and modularity in the web application code, making it easier to maintain and scale over time.
Example of using the Repository pattern with a database
In the Repository pattern, the database is represented as a collection of objects, with each object representing a table or collection in the database. The Repository class provides a set of methods for interacting with the database, such as creating, reading, updating, and deleting objects.
For example, suppose we have an Express application that stores information about books in a database. We can create a Book model that defines the fields and behavior of a book object. We can then create a BookRepository class that provides methods for creating, reading, updating, and deleting book objects in the database.
In the BookRepository class, we can define methods such as get_all_books and get_book_by_id that retrieve book objects from the database. We can also define methods such as create_book and update_book that add or modify book objects in the database.
Using the Repository pattern with a database can provide a number of benefits, including improved testability, maintainability, and flexibility.
By abstracting the database access layer from the rest of the application, developers can easily switch between different database technologies or change the database schema without affecting the rest of the application. Also, by providing a set of methods for interacting with the database, the Repository pattern can make it easier to write tests for the application.
In the following example, we define a Book interface that represents a book object with an ID, title, author, and published date. We also define a BookRepository class that provides methods for interacting with a database of books, using a database connection object to execute SQL queries.
We then demonstrate how to use the BookRepository class to perform common CRUD operations on the database, including getting all books, getting a book by its ID, creating a new book, updating an existing book, and deleting a book.
// Define a Book interface that represents a book object
interface Book {
id: number;
title: string;
author: string;
publishedDate: Date;
}
// Define a BookRepository class that provides methods for interacting with a database of books
class BookRepository {
private db: any; // Database connection object
constructor(db: any) {
this.db = db;
}
// Get all books from the database
async getAllBooks(): Promise<Book[]> {
const result = await this.db.query('SELECT * FROM books');
return result.rows;
}
// Get a book by its ID
async getBookById(id: number): Promise<Book> {
const result = await this.db.query('SELECT * FROM books WHERE id = $1', [id]);
return result.rows[0];
}
// Create a new book in the database
async createBook(book: Book): Promise<void> {
await this.db.query('INSERT INTO books (title, author, published_date) VALUES ($1, $2, $3)', [book.title, book.author, book.publishedDate]);
}
// Update an existing book in the database
async updateBook(id: number, book: Book): Promise<void> {
await this.db.query('UPDATE books SET title = $1, author = $2, published_date = $3 WHERE id = $4', [book.title, book.author, book.publishedDate, id]);
}
// Delete a book from the database
async deleteBook(id: number): Promise<void> {
await this.db.query('DELETE FROM books WHERE id = $1', [id]);
}
}
// Example usage of the BookRepository class
const db = new Database(); // Instantiate a database connection object
const bookRepository = new BookRepository(db); // Instantiate a BookRepository object
const books = await bookRepository.getAllBooks(); // Get all books from the database
const book = await bookRepository.getBookById(1); // Get a book by its ID
const newBook = { title: 'New Book', author: 'Jane Doe', publishedDate: new Date() };
await bookRepository.createBook(newBook); // Create a new book in the database
await bookRepository.updateBook(1, { title: 'Updated Book', author: 'John Smith', publishedDate: new Date() }); // Update an existing book in the database
await bookRepository.deleteBook(1); // Delete a book from the database
Example of using the Dependency Injection pattern for decoupling dependencies
In the context of backend development, we can use Dependency Injection to decouple our application’s components from the specific implementation of external services or libraries, such as databases, caches, or email providers. This allows us to easily switch between different implementations of these services, or to mock them during testing.
Here’s an example of using Dependency Injection in a TypeScript application that interacts with a database:
// Define an interface for a database connection object
interface DatabaseConnection {
query(sql: string, params?: any[]): Promise<any>;
}
// Define a class for a PostgreSQL database connection
class PostgresConnection implements DatabaseConnection {
private client: any; // PostgreSQL client object
constructor() {
this.client = new PostgreSQLClient(); // Instantiate a PostgreSQL client object
this.client.connect(); // Connect to the database
}
async query(sql: string, params?: any[]): Promise<any> {
const result = await this.client.query(sql, params);
return result.rows;
}
}
// Define a class for a BookService that depends on a database connection
class BookService {
private db: DatabaseConnection; // Database connection object
constructor(db: DatabaseConnection) {
this.db = db;
}
async getAllBooks(): Promise<Book[]> {
const result = await this.db.query('SELECT * FROM books');
return result.map((row: any) => ({ id: row.id, title: row.title, author: row.author, publishedDate: row.published_date }));
}
async getBookById(id: number): Promise<Book> {
const result = await this.db.query('SELECT * FROM books WHERE id = $1', [id]);
return { id: result.id, title: result.title, author: result.author, publishedDate: result.published_date };
}
async createBook(book: Book): Promise<void> {
await this.db.query('INSERT INTO books (title, author, published_date) VALUES ($1, $2, $3)', [book.title, book.author, book.publishedDate]);
}
async updateBook(id: number, book: Book): Promise<void> {
await this.db.query('UPDATE books SET title = $1, author = $2, published_date = $3 WHERE id = $4', [book.title, book.author, book.publishedDate, id]);
}
async deleteBook(id: number): Promise<void> {
await this.db.query('DELETE FROM books WHERE id = $1', [id]);
}
}
// Example usage of the BookService class with a PostgresConnection object
const db = new PostgresConnection(); // Instantiate a PostgresConnection object
const bookService = new BookService(db); // Instantiate a BookService object with the PostgresConnection object as its dependency
const books = await bookService.getAllBooks(); // Get all books from the database
const book = await bookService.getBookById(1); // Get a book by its ID
const newBook = { title: 'New Book', author: 'Jane Doe', publishedDate: new Date() };
await bookService.createBook(newBook); // Create a new book in the database
await bookService.updateBook(1, { title: 'Updated Book', author: 'John Smith', publishedDate: new Date() }); //
Example of using the Observer pattern for event-driven programming
Suppose we have a web application that allows users to subscribe to different topics of interest. Whenever new content is added to a subscribed topic, the user receives a notification. We can implement this feature using the Observer pattern.
First, we define our subject interface Topic, which will notify its observers (subscribers) of any updates:
interface Topic {
subscribe(observer: Observer): void;
unsubscribe(observer: Observer): void;
notify(): void;
}Then we implement the Topic interface in a concrete subject class, TopicManager, which manages a list of subscribers and notifies them whenever new content is added:
class TopicManager implements Topic {
private subscribers: Observer[] = [];
public subscribe(observer: Observer): void {
this.subscribers.push(observer);
}
public unsubscribe(observer: Observer): void {
const index = this.subscribers.indexOf(observer);
if (index !== -1) {
this.subscribers.splice(index, 1);
}
}
public notify(): void {
for (const subscriber of this.subscribers) {
subscriber.update();
}
}
public addContent(topic: string, content: string): void {
// Add new content to the topic
// ...
// Notify all subscribers of the new content
this.notify();
}
}
Next, we define our observer interface Observer, which has an update method that will be called by the subject:
interface Observer {
update(): void;
}We then implement the Observer interface in a concrete observer class, User, which receives notifications when new content is added to a subscribed topic:
class User implements Observer {
private readonly username: string;
constructor(username: string) {
this.username = username;
}
public update(): void {
console.log(`[${this.username}] New content has been added to a subscribed topic`);
}
}
Finally, we can use our TopicManager and User classes to implement our subscription feature:
// Create a new topic manager
const topicManager = new TopicManager();
// Create two users
const user1 = new User('Alice');
const user2 = new User('Bob');
// Subscribe the users to a topic
topicManager.subscribe(user1);
topicManager.subscribe(user2);
// Add new content to the topic
topicManager.addContent('science', 'New scientific discovery!');
// Output:
// [Alice] New content has been added to a subscribed topic
// [Bob] New content has been added to a subscribed topicIn this example, the TopicManager acts as the subject and the User class acts as the observer.
The TopicManager maintains a list of subscribers and notifies them whenever new content is added to a subscribed topic. The User class receives notifications and performs some actions, such as displaying a notification to the user.
The Observer pattern allows us to decouple the subject and observers, making it easy to add or remove subscribers without affecting the rest of the system.
Example of using the Decorator pattern for adding functionality to a class dynamically
Suppose we have a class Car that represents a basic car with some properties and methods:
class Car {
private make: string;
private model: string;
private year: number;
private price: number;
constructor(make: string, model: string, year: number, price: number) {
this.make = make;
this.model = model;
this.year = year;
this.price = price;
}
public getMake(): string {
return this.make;
}
public getModel(): string {
return this.model;
}
public getYear(): number {
return this.year;
}
public getPrice(): number {
return this.price;
}
}
We want to add some additional functionality to this class, such as the ability to calculate the sales tax on the car price and to add some optional features to the car, such as a navigation system and a sunroof. We can use the Decorator pattern to add these features dynamically to the Car class.
First, we define an abstract base class CarFeature that all decorators will inherit from:
abstract class CarFeature extends Car {
protected car: Car;
constructor(car: Car) {
super(car.getMake(), car.getModel(), car.getYear(), car.getPrice());
this.car = car;
}
public abstract getPrice(): number;
}
Next, we implement concrete decorator classes that add the desired functionality to the Car class:
class SalesTaxDecorator extends CarFeature {
public getPrice(): number {
return this.car.getPrice() * 1.10; // 10% sales tax
}
}
class NavigationDecorator extends CarFeature {
public getPrice(): number {
return this.car.getPrice() + 1500; // add $1500 for navigation system
}
}
class SunroofDecorator extends CarFeature {
public getPrice(): number {
return this.car.getPrice() + 1000; // add $1000 for sunroof
}
}
We can then use these decorators to add functionality to a Car object dynamically:
// Create a basic car
const car = new Car('Honda', 'Accord', 2022, 25000);
// Add sales tax to the car
const carWithSalesTax = new SalesTaxDecorator(car);
// Add a navigation system to the car
const carWithNavigation = new NavigationDecorator(carWithSalesTax);
// Add a sunroof to the car
const carWithSunroof = new SunroofDecorator(carWithNavigation);
console.log(`Make: ${carWithSunroof.getMake()}`);
console.log(`Model: ${carWithSunroof.getModel()}`);
console.log(`Year: ${carWithSunroof.getYear()}`);
console.log(`Price: ${carWithSunroof.getPrice()}`);
// Output:
// Make: Honda
// Model: Accord
// Year: 2022
// Price: 28750In this example, we use the Decorator pattern to add functionality to a Car object dynamically. Each decorator extends the CarFeature abstract class and adds some additional functionality to the Car object.
We can add multiple decorators to a Car object in any order, and each decorator adds its own functionality to the object. This allows us to create highly customized Car objects with only the features we need while keeping the core Car class simple and easy to maintain.
Conclusion
Design patterns are essential in modern backend development as they provide a structured approach to solving common problems. The use of design patterns offers numerous advantages, including code reusability, scalability, maintainability, reduced errors, and improved performance.
In this tutorial, we discussed some of the most common design patterns used in backend development, including MVC, Repository, Dependency Injection, Observer, and Decorator. We have also provided real-world examples of these patterns in action, along with code samples in TypeScript.
By understanding and implementing these patterns in their development work, developers can write maintainable, scalable, and efficient code that can easily adapt to changing requirements.
Overall, the use of design patterns in backend development is essential for creating high-quality, robust applications that can withstand the test of time.
Next Steps
If you are a backend developer looking to master design patterns, there are several steps you can take to improve your knowledge and skills:
- Read books and articles on design patterns: There are numerous books and articles available on design patterns, and reading them can help you understand the concepts and principles behind them (I have pinned some of them in the next section).
- Practice implementing design patterns: Implementing design patterns in your day to day work is the best way to learn them. Start by incorporating one or two patterns into your projects and gradually work your way up to more complex patterns.
- Keep learning: Design patterns are not a one-time thing – they are continually evolving. To stay up-to-date with the latest patterns and best practices, you need to keep learning and experimenting.
- Join online communities: There are many online communities where developers discuss design patterns and share their knowledge and experience. Joining these communities can be a great way to learn from others and to ask for help when you need it.
- Attend workshops and conferences: Attending workshops and conferences focused on design patterns can provide a deep understanding of how they work and how to implement them effectively.
By following these steps, you can become an expert in design patterns and write high-quality, maintainable, and scalable code for your backend applications.
Resources
- “Design Patterns: Elements of Reusable Object-Oriented Software” by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides
- “Head First Design Patterns” by Eric Freeman, Elisabeth Robson, Bert Bates, and Kathy Sierra
- “Clean Code: A Handbook of Agile Software Craftsmanship” by Robert C. Martin
- “Dependency Injection: Principles, Practices, and Patterns” by Steven van Deursen and Mark Seemann
- Three Types of Design Patterns All Devs Should Know
- The Repository Pattern from the Microsoft Docs
- Decorator Pattern in TypeScript
- The Benefits of Using Design Patterns in Software Development
