What is the Repository pattern?

Repository pattern abstracts data access, providing collection-like interface for domain objects. Acts as in-memory collection while hiding database details. Methods: findById, findAll, save, delete. Benefits: decouples domain from persistence, enables testing with mock repositories, supports swapping storage implementations, centralizes query logic. Often combined with Unit of Work (transaction management). ORMs like Spring Data, Django ORM implement repository concepts. Avoid: repository returning DTOs, business logic in repositories.