Repository Pattern (Architecture)

ELI5 — The Vibe Check

The repository pattern makes your database look like an in-memory collection. Instead of writing SQL, you call repository.findById(42) or repository.save(order). The actual database query is hidden behind the curtain. Your domain stays database-ignorant.

Real Talk

A design pattern that mediates between the domain model and data mapping layers, providing a collection-like interface for accessing domain objects. Repositories encapsulate the logic for querying and persisting aggregates, allowing the domain layer to remain infrastructure-agnostic. Often used with Unit of Work pattern.

Show Me The Code

interface OrderRepository {
  findById(id: string): Promise<Order | null>;
  save(order: Order): Promise<void>;
  findByCustomer(customerId: string): Promise<Order[]>;
}

class PostgresOrderRepository implements OrderRepository {
  async findById(id: string) {
    const row = await this.db.query('SELECT * FROM orders WHERE id = $1', [id]);
    return row ? this.toDomain(row) : null;
  }
}

When You'll Hear This

"The repository returns domain objects, not database rows — it handles all the mapping." / "Use an in-memory repository for unit tests so you don't need a running database."