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What is the Repository pattern and how does it decouple business logic from the database?

Q: What is the Repository pattern and how does it decouple business logic from the database?

**TL;DR.** The **Repository pattern** hides data access behind an **interface** (e.g. UserRepository.findById ), so business logic depends on the **abstraction**, not on SQL or a specific ORM. This makes services **testable** with in-memory fakes and lets you **swap** the data store without touching domain code. service Repository interface <path class='d-edge-dashed'

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Understand the problem

Abstracting persistence behind an interface.

nodejsarchitecturerepository-patterndesign

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Interface + two implementations

// service depends on the shape, not the DB
class UserService {
  constructor(repo) { this.repo = repo; }
  async promote(id) { const u = await this.repo.findById(id); u.role = 'admin'; await this.repo.save(u); }
}

// prod impl
class PgUserRepo { async findById(id) { /* SQL */ } async save(u) { /* SQL */ } }
// test impl — no DB needed
class FakeUserRepo { users = new Map(); async findById(id){return this.users.get(id);} async save(u){this.users.set(u.id,u);} }

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