DDD Repository Patterns

The Repository Pattern is a design pattern that mediates data access to the domain and data mapping layers. It acts as a collection of domain objects, providing methods for adding, removing, and querying these objects.

The key concepts of the Repository Pattern include:

• Encapsulation of data access logic.
• Separation of concerns between the domain and data layers.
• Providing a collection-like interface for accessing domain objects.

Step 1: Define the Repository Interface

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

Step 2: Implement the Repository

public class Repository<T> : IRepository<T> {
    private readonly List<T> _entities = new List<T>();

    public void Add(T entity) {
        _entities.Add(entity);
    }

    public void Remove(T entity) {
        _entities.Remove(entity);
    }

    public T FindById(int id) {
        return _entities.FirstOrDefault(e => (e as dynamic).Id == id);
    }

    public IEnumerable<T> GetAll() {
        return _entities;
    }
}

To effectively implement the Repository Pattern, consider the following best practices:

1. Keep repositories focused on a specific aggregate root.
2. Use Dependency Injection to manage repository lifetimes.
3. Avoid exposing IQueryable to ensure that the domain model remains pure.