Singleton Pattern in NestJS

Overview

Ensure a class has only one instance

Singleton Pattern 2 implementations available

When to Use

When you need to abstract data access logic
When you want to make your code testable
When you need to support multiple data sources
When you want to decouple business logic from infrastructure

Available Implementations

Public Route

Mark routes as public to skip auth

npx hanma add public --framework nest

Skip auth guardsWorks with global guardsSimple metadata decorator

HTTP Exception Filter

Global HTTP exception handling

npx hanma add http-exception-filter --framework nest

Structured error responseRequest ID includedStatus-based logging

Basic Example

// Singleton Pattern implementation example
// This shows the basic structure of singleton pattern in NestJS

// Define your interface
interface IRepository {
  findAll(): Promise<T[]>;
  findById(id: string): Promise<T | null>;
  create(data: CreateDto): Promise<T>;
  update(id: string, data: UpdateDto): Promise<T>;
  delete(id: string): Promise<void>;
}

// Implement the pattern
class SingletonRepository implements IRepository {
  async findAll(): Promise<T[]> {
    // Implementation
  }

  async findById(id: string): Promise<T | null> {
    // Implementation
  }

  async create(data: CreateDto): Promise<T> {
    // Implementation
  }

  async update(id: string, data: UpdateDto): Promise<T> {
    // Implementation
  }

  async delete(id: string): Promise<void> {
    // Implementation
  }
}

// Use the pattern
const repository = new SingletonRepository();
const items = await repository.findAll();

Frequently Asked Questions

What is Singleton Pattern?

Ensure a class has only one instance. It's a well-established software design pattern that helps organize code for better maintainability and testability.

How does Singleton Pattern work with NestJS?

NestJS provides excellent support for this pattern through its dependency injection system and middleware composition.

What are the benefits?

Improved testability, separation of concerns, easier maintenance, and flexibility to change implementations without affecting business logic.

When should I avoid this pattern?

For very simple applications with minimal logic, the pattern may add unnecessary complexity. Use judgment based on project requirements.