Dependency Inversion Principle

1. ProductServiceBeforeDIP

namespace ConsoleApplication1
{
    public class ProductServiceBeforeDIP
    {
        LinqToSqlProductRepository _productRepository;

        public ProductServiceBeforeDIP()
        {
            _productRepository = new LinqToSqlProductRepository();
        }
    }
}

1. ProductServiceAfterDIP

namespace ConsoleApplication1
{
    class ProductServiceAfterDIP
    {
        IProductRepository _productRepository;

        // using constructor to passing dependecy
        public ProductServiceAfterDIP(IProductRepository productRepository)
        {
            _productRepository = productRepository;
        }

        public void GetAll()
        {
            // getting data
        }
    }

    public interface IProductRepository
    {
        void GetAll();
    }
}

1. Demo

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            //1. using LinqToSql as data provider
            ProductServiceAfterDIP productService = new ProductServiceAfterDIP(new LinqToSqlProductRepository());

            productService.GetAll();

            //2. using EF as data provider
            productService = new ProductServiceAfterDIP(new EntityFrameWorkProductRepository());

            productService.GetAll();
        }
    }

    public class EntityFrameWorkProductRepository : IProductRepository
    {
        #region IProductRepository Members

        public void GetAll()
        {
            // getting data with ef
        }

        #endregion
    }

    public class LinqToSqlProductRepository : IProductRepository
    {
        #region IProductRepository Members

        public void GetAll()
        {
            // getting data with LinQtoSql
        }

        #endregion
    }
}