Repository

Context: Mediate between the domain and data mapping layers using a collection‑like interface for accessing domain objects.

public interface IRepository<T>
{
    T GetById(int id);
    IEnumerable<T> GetAll();
    void Add(T entity);
    void Remove(T entity);
}

public class InMemoryRepository<T> : IRepository<T>
{
    private List<T> _data = new();
    public T GetById(int id) => _data.FirstOrDefault(e => e.GetHashCode() == id);
    public IEnumerable<T> GetAll() => _data;
    public void Add(T entity) => _data.Add(entity);
    public void Remove(T entity) => _data.Remove(entity);
}

Real-world usage example

Data access abstraction: An application uses IRepository<Customer>; the implementation can be Entity Framework, Dapper, or a mock for unit tests. Business logic is decoupled from data source.

Example: In ASP.NET Core, generic IRepository<T> is often used with EF Core’s DbSet<T>. The repository pattern is common in clean architecture / DDD.

Related sections

• 5.4 Architectural patterns for backend
• 5.4.2 Middleware