Stop Spaghetti Code: Why Backend Developers Need the Repository Pattern

Insight: Spaghetti code is more than just messy syntax; it’s a structural anti‑pattern that hampers scalability and team velocity.

What You Will Learn

• Identify the warning signs of spaghetti code in backend services.
• Understand the core principles of the Repository Pattern.
• Apply a clean, testable repository implementation in a real‑world Node.js project.
• Evaluate the trade‑offs and when to adopt the pattern.

Understanding Spaghetti Code

Symptoms

• Tight coupling between business logic and data access.
• Scattered raw SQL or ORM queries across the codebase.
• Difficulty writing unit tests due to hidden dependencies.

Consequences

• Reduced maintainability – a small change can break unrelated features.
• Slower onboarding – new developers spend hours tracing data flow.
• Higher bug surface – regression bugs become common.

The Repository Pattern Explained

Core Concepts

The Repository Pattern acts as an abstraction layer between the domain and data mapping layers. It provides a collection‑like interface for accessing domain objects.

interface UserRepository {
  findById(id: string): Promise<User>;
  findAll(): Promise<User[]>;
  save(user: User): Promise<void>;
  delete(id: string): Promise<void>;
}

Benefits

• Separation of Concerns – business logic no longer knows how data is persisted.
• Testability – repositories can be mocked or swapped with in‑memory implementations.
• Flexibility – switch databases or ORMs without touching the core logic.

How the Repository Pattern Works

The following diagram illustrates the flow of data and dependencies in the Repository Pattern:

classDiagram
  class DomainModel {
    +id: string
    +data: any
  }
  class Repository {
    +findById(id: string): DomainModel
    +findAll(): DomainModel[]
    +save(model: DomainModel): void
    +delete(id: string): void
  }
  class DataService {
    +getData(): any
  }
  class BusinessLogic {
    -repository: Repository
    +performAction(): void
  }
  DomainModel --* Repository : uses
  Repository --* DataService : uses
  BusinessLogic --* Repository : uses

This diagram shows how the Domain Model is decoupled from the Data Service through the Repository. The Business Logic layer interacts with the Repository, which in turn uses the Data Service to access the data.

Implementing the Repository Pattern in Node.js

Example Code

Below is a minimal implementation using TypeScript and TypeORM.

// src/repositories/UserRepositoryImpl.ts
import { getRepository } from "typeorm";
import { User } from "../entities/User";
import { UserRepository } from "./UserRepository";

export class UserRepositoryImpl implements UserRepository {
  private ormRepo = getRepository(User);

  async findById(id: string): Promise<User | undefined> {
    return this.ormRepo.findOne(id);
  }

  async findAll(): Promise<User[]> {
    return this.ormRepo.find();
  }

  async save(user: User): Promise<void> {
    await this.ormRepo.save(user);
  }

  async delete(id: string): Promise<void> {
    await this.ormRepo.delete(id);
  }
}

Tip: Inject UserRepository into your service classes via constructor injection to keep them agnostic of the underlying data source.

Service Usage

// src/services/UserService.ts
import { UserRepository } from "../repositories/UserRepository";

export class UserService {
  constructor(private readonly userRepo: UserRepository) {}

  async getUserProfile(id: string) {
    const user = await this.userRepo.findById(id);
    if (!user) throw new Error("User not found");
    return { id: user.id, name: user.name, email: user.email };
  }
}

When Not to Use the Repository Pattern

• Simple CRUD micro‑services where the overhead outweighs benefits.
• Performance‑critical paths that require fine‑grained query optimization (you can still use a repository but expose query methods).

Conclusion

Adopting the Repository Pattern is a proven strategy to eliminate spaghetti code, boost testability, and future‑proof your backend architecture. Start refactoring one module at a time, and watch your codebase become more maintainable and scalable.

Ready to clean up your code? Try implementing a repository in your next feature and experience the difference.