我对petshop4的简单理解！

petshop4充分体现了面向接口编程的思想，就是给你一个接口你别管我是怎么实现的，你只管用别说其他的。

namespace PetShop.BLL {

    /// <summary>    /// A business component to manage products    /// </summary>    public class Product {

        // Get an instance of the Product DAL using the DALFactory        // Making this static will cache the DAL instance after the initial load        private static readonly IProduct dal = PetShop.DALFactory.DataAccess.CreateProduct();

在bll层，这里使用创建Produce的接口，你只管调用他的方法。

namespace PetShop.IDAL{  /// <summary> /// Interface for the Product DAL /// </summary> public interface IProduct{   /// <summary>  /// Method to search products by category name  /// </summary>  /// <param name="category">Name of the category to search by</param>        /// <returns>Interface to Model Collection Generic of search results</returns>  IList<ProductInfo> GetProductsByCategory(string category); 

  /// <summary>  /// Method to search products by a set of keyword  /// </summary>  /// <param name="keywords">An array of keywords to search by</param>  /// <returns>Interface to Model Collection Generic of search results</returns>        IList<ProductInfo> GetProductsBySearch(string[] keywords);

  /// <summary>  /// Query for a product  /// </summary>  /// <param name="productId">Product Id</param>  /// <returns>Interface to Model ProductInfo for requested product</returns>  ProductInfo GetProduct(string productId); }

这里是定义了Product接口和他的虚方法。

namespace PetShop.SQLServerDAL {

    public class Product : IProduct {

        //Static constants        private const string SQL_SELECT_PRODUCTS_BY_CATEGORY = "SELECT Product.ProductId, Product.Name, Product.Descn, Product.Image, Product.CategoryId FROM Product WHERE Product.CategoryId = @Category";        private const string SQL_SELECT_PRODUCTS_BY_SEARCH1 = "SELECT ProductId, Name, Descn, Product.Image, Product.CategoryId FROM Product WHERE ((";        private const string SQL_SELECT_PRODUCTS_BY_SEARCH2 = "LOWER(Name) LIKE '%' + {0} + '%' OR LOWER(CategoryId) LIKE '%' + {0} + '%'";        private const string SQL_SELECT_PRODUCTS_BY_SEARCH3 = ") OR (";        private const string SQL_SELECT_PRODUCTS_BY_SEARCH4 = "))";        private const string SQL_SELECT_PRODUCT = "SELECT Product.ProductId, Product.Name, Product.Descn, Product.Image, Product.CategoryId FROM Product WHERE Product.ProductId  = @ProductId";        private const string PARM_CATEGORY = "@Category";        private const string PARM_KEYWORD = "@Keyword";        private const string PARM_PRODUCTID = "@ProductId";

        /// <summary>        /// Query for products by category        /// </summary>        /// <param name="category">category name</param>          /// <returns>A Generic List of ProductInfo</returns>        public IList<ProductInfo> GetProductsByCategory(string category) {

            IList<ProductInfo> productsByCategory = new List<ProductInfo>();

这里是实现Product接口的类，

namespace PetShop.DALFactory {

    /// <summary>    /// This class is implemented following the Abstract Factory pattern to create the DAL implementation    /// specified from the configuration file    /// </summary>    public sealed class DataAccess {

        // Look up the DAL implementation we should be using        private static readonly string path = ConfigurationManager.AppSettings["WebDAL"];        private static readonly string orderPath = ConfigurationManager.AppSettings["OrdersDAL"];                private DataAccess() { }

        public static PetShop.IDAL.ICategory CreateCategory() {            string className = path + ".Category";            return (PetShop.IDAL.ICategory)Assembly.Load(path).CreateInstance(className);        }

这里是利用工厂模式来映射你需要你想创建哪一个。

后面还有一些消息队列MSMQMessage利用cache缓存以后达到异步处理购物车里订单的功能！

刚开始看应先从先从Product入口，关于Product的一些操作串联起来看一遍！