《大话设计模式》学习笔记11：抽象工厂模式

切换数据库类型示例：

1.User类：

    public class User
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }

2.AbstractProduct（以User为例）：

    public interface IUser
    {
        void Insert(User user);
        User GetUser(int id);
    }

3.Product（以User、SQL Server为例）：

    public class SqlserverUser:IUser
    {
        public void Insert(User user)
        {
            Console.WriteLine("在SQL Server中给User表增加一条记录");
        }

        public User GetUser(int id)
        {
            Console.WriteLine("在SQL Server中根据Id得到User表中的一条记录");
            return null;
        }
    }

4.AbstractFactory：

    public interface IFactory
    {
        IUser CreateUser();
        IDepartment CreateDepartment();
    }

5.ConcreteFactory（以SQL Server为例）：

    public class SqlserverFactory:IFactory
    {
        public IUser CreateUser()
        {
            return new SqlserverUser();
        }
        public IDepartment CreateDepartment()
        {
            return new SqlserverDepartment();
        }
    }

6.客户端代码：

    class Program
    {
        static void Main(string[] args)
        {
            IFactory factory = new SqlserverFactory();
            IUser user = factory.CreateUser();
            user.Insert(new User());
            user.GetUser(1);
        }
    }

用简单工厂来改进抽象工厂：

1.DataAccess：

    public class DataAccess
    {
        private static readonly string db = "Sqlserver";
        //private static readonly string db = "Access";
        public static IUser CreateUser()
        {
            IUser user;
            switch (db)
            {
                case "Sqlserver":
                    user = new SqlserverUser();
                    break;
                case "Access":
                    user = new AccessUser();
                    break;
            }
            return user;
        }

        public static IDepartment CreateDepartment()
        {
            IDepartment department;
            switch (db)
            {
                case "Sqlserver":
                    department = new SqlserverDepartment();
                    break;
                case "Access":
                    department = new AccessDepartment();
                    break;
            }
            return department;
        }
    }

2.客户端代码：

    class Program
    {
        static void Main(string[] args)
        {
            IUser user = DataAccess.CreateUser();
            user.Insert(new User());
            user.GetUser(1);
        }
    }

反射+抽象工厂：

DataAccess：

using System.Reflection;

    public class DataAccess
    {
        private static readonly string AssemblyName = "AbstractFactory";//程序集名称
        private static readonly string db = "Sqlserver";//数据库类型
        public static IUser CreateUser()
        {
            string className = AssemblyName + "." + db + "User";
            return (IUser)Assembly.Load(AssemblyName).CreateInstance(className);
        }

        public static IDepartment CreateDepartment()
        {
            string className = AssemblyName + "." + db + "Department";
            return (IDepartment)Assembly.Load(AssemblyName).CreateInstance(className);
        }
    }

反射+配置文件：

1.配置文件：

<configuration>
  <appSettings>
    <add key="DB" value="Sqlserver"/>
  </appSettings>
</configuration>

2.DataAccess：

using System.Configuration; 

    public class DataAccess
    {
        private static readonly string AssemblyName = "AbstractFactory";//程序集名称
        private static readonly string db = ConfigurationManager.AppSettings["DB"];
        public static IUser CreateUser()
        {
            string className = AssemblyName + "." + db + "User";
            return (IUser)Assembly.Load(AssemblyName).CreateInstance(className);
        }

        public static IDepartment CreateDepartment()
        {
            string className = AssemblyName + "." + db + "Department";
            return (IDepartment)Assembly.Load(AssemblyName).CreateInstance(className);
        }
    }