就不能换DB吗？ 抽象工厂模式

15.1 就不能换DB吗？

15.2 最基本的数据访问程序

namespace 抽象工厂模式
{
    class Program
    {
        static void Main(string[] args)
        {
            User user = new User();

            SqlserverUser su = new SqlserverUser();   //与SQLServer耦合，

            su.Insert(user);
            su.GetUser(1);

            Console.Read();
        }
    }

    //用户类，
    class User
    {
        private int _id;

        public int ID
        {
            get { return _id; }
            set { _id = value; }
        }

        private string _name;

        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }
    }

    //操作User表类，
    class SqlserverUser
    {
        //新增用户，
        public void Insert(User user)
        {
            Console.WriteLine("在Sqlserver中给User表增加一条记录");
        }

        //得到用户，
        public User GetUser(int id)
        {
            Console.WriteLine("在Sqlserver中根据ID得到User表一条记录");
            return null;
        }
    }

}

15.3 用了工厂方法模式的数据访问程序

namespace 抽象工厂模式
{
    class Program
    {
        static void Main(string[] args)
        {
            User user = new User();

            //IFactory factory = new SqlServerFactory();
            IFactory factory = new AccessFactory();

            IUser iu = factory.CreateUser();

            iu.Insert(user);
            iu.GetUser(1);

            Console.Read();
        }
    }

    class User
    {
        private int _id;

        public int ID
        {
            get { return _id; }
            set { _id = value; }
        }

        private string _name;

        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }
    }

    //IUser接口，用于客户端访问，解除与具体数据库的耦合，
    interface IUser
    {
        void Insert(User user);

        User GetUser(int id);
    }

    //SqlserverUser类，用于访问SQLServer的User，
    class SqlserverUser : IUser
    {
        public void Insert(User user)
        {
            Console.WriteLine("在Sqlserver中给User表增加一条记录");
        }

        public User GetUser(int id)
        {
            Console.WriteLine("在Sqlserver中根据ID得到User表一条记录");
            return null;
        }
    }

    //AccessUser类，用于访问Access的User，
    class AccessUser : IUser
    {
        public void Insert(User user)
        {
            Console.WriteLine("在Access中给User表增加一条记录");
        }

        public User GetUser(int id)
        {
            Console.WriteLine("在Access中根据ID得到User表一条记录");
            return null;
        }
    }

    //IFactory接口，定义一个创建访问User表对象的抽象的工厂接口，
    interface IFactory
    {
        IUser CreateUser();
    }

    //SqlServerFactory类，实现IFactory接口，实例化SqlserverUser，
    class SqlServerFactory : IFactory
    {
        public IUser CreateUser()
        {
            return new SqlserverUser();
        }
    }

    //AccessFactory类，实现IFactory接口，实例化AccessUser，
    class AccessFactory : IFactory
    {
        public IUser CreateUser()
        {
            return new AccessUser();
        }
    }

}

15.4 用了抽象工厂模式的数据访问程序

namespace 抽象工厂模式
{
    class Program
    {
        static void Main(string[] args)
        {
            User user = new User();
            Department dept = new Department();

            //IFactory factory = new SqlServerFactory();
            IFactory factory = new AccessFactory();

            IUser iu = factory.CreateUser();
            iu.Insert(user);
            iu.GetUser(1);

            IDepartment id = factory.CreateDepartment();
            id.Insert(dept);
            id.GetDepartment(1);

            Console.Read();
        }
    }

    class User
    {
        private int _id;

        public int ID
        {
            get { return _id; }
            set { _id = value; }
        }

        private string _name;

        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }
    }

    class Department
    {
        private int _id;

        public int ID
        {
            get { return _id; }
            set { _id = value; }
        }

        private string _deptName;

        public string DeptName
        {
            get { return _deptName; }
            set { _deptName = value; }
        }
    }

    interface IUser
    {
        void Insert(User user);

        User GetUser(int id);
    }

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

        public User GetUser(int id)
        {
            Console.WriteLine("在Sqlserver中根据ID得到User表一条记录");
            return null;
        }
    }

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

        public User GetUser(int id)
        {
            Console.WriteLine("在Access中根据ID得到User表一条记录");
            return null;
        }
    }

    interface IDepartment
    {
        void Insert(Department department);

        Department GetDepartment(int id);
    }

    class SqlserverDepartment : IDepartment
    {
        public void Insert(Department department)
        {
            Console.WriteLine("在Sqlserver中给Department表增加一条记录");
        }

        public Department GetDepartment(int id)
        {
            Console.WriteLine("在Sqlserver中根据ID得到Department表一条记录");
            return null;
        }
    }

    class AccessDepartment : IDepartment
    {
        public void Insert(Department department)
        {
            Console.WriteLine("在Access中给Department表增加一条记录");
        }

        public Department GetDepartment(int id)
        {
            Console.WriteLine("在Access中根据ID得到Department表一条记录");
            return null;
        }
    }

    interface IFactory
    {
        IUser CreateUser();

        IDepartment CreateDepartment();
    }

    class SqlServerFactory : IFactory
    {
        public IUser CreateUser()
        {
            return new SqlserverUser();
        }

        public IDepartment CreateDepartment()
        {
            return new SqlserverDepartment();
        }
    }

    class AccessFactory : IFactory
    {
        public IUser CreateUser()
        {
            return new AccessUser();
        }

        public IDepartment CreateDepartment()
        {
            return new AccessDepartment();
        }
    }

}

15.5 抽象工厂模式

提供一个创建一系列相关或相互依赖对象的接口，而无需指定它们具体的类，

namespace 抽象工厂模式
{
    class Program
    {
        static void Main(string[] args)
        {
            AbstractFactory factory1 = new ConcreteFactory1();
            Client c1 = new Client(factory1);
            c1.Run();

            AbstractFactory factory2 = new ConcreteFactory2();
            Client c2 = new Client(factory2);
            c2.Run();

            Console.Read();
        }
    }

    //抽象产品A，
    abstract class AbstractProductA
    {
        //它们可以有不同的实现，
    }

    //抽象产品B，
    abstract class AbstractProductB
    {
        public abstract void Interact(AbstractProductA a);
    }

    //对两个抽象产品A和B的具体分类的实现，
    class ProductA1 : AbstractProductA
    {

    }

    //对两个抽象产品A和B的具体分类的实现，
    class ProductB1 : AbstractProductB
    {
        public override void Interact(AbstractProductA a)
        {
            Console.WriteLine(this.GetType().Name + " interacts with " + a.GetType().Name);
        }
    }

    //对两个抽象产品A和B的具体分类的实现，
    class ProductA2 : AbstractProductA
    {

    }

    //对两个抽象产品A和B的具体分类的实现，
    class ProductB2 : AbstractProductB
    {
        public override void Interact(AbstractProductA a)
        {
            Console.WriteLine(this.GetType().Name + " interacts with " + a.GetType().Name);
        }
    }

    //抽象工厂接口，包含所有产品创建的抽象方法，
    abstract class AbstractFactory
    {
        public abstract AbstractProductA CreateProductA();
        public abstract AbstractProductB CreateProductB();
    }

    //具体工厂，
    class ConcreteFactory1 : AbstractFactory
    {
        public override AbstractProductA CreateProductA()
        {
            return new ProductA1();
        }

        public override AbstractProductB CreateProductB()
        {
            return new ProductB1();
        }
    }

    //具体工厂，
    class ConcreteFactory2 : AbstractFactory
    {
        public override AbstractProductA CreateProductA()                      //运行时创建ConcreteFactory类的实例，具体的工厂再创建具有特定实现的产品对象，
        {                                                                      //即创建不同的产品对象，客户端应使用不同的具体工厂，
            return new ProductA2();
        }

        public override AbstractProductB CreateProductB()
        {
            return new ProductB2();
        }
    }

    class Client
    {
        private AbstractProductA AbstractProductA;
        private AbstractProductB AbstractProductB;

        public Client(AbstractFactory factory)
        {
            AbstractProductB = factory.CreateProductB();
            AbstractProductA = factory.CreateProductA();
        }

        public void Run()
        {
            AbstractProductB.Interact(AbstractProductA);
        }
    }

}

15.6 抽象工厂模式的优点与缺点

优点：最大的好处便是易于交换产品系列，由于具体工厂类，在一个应用中只需要在初始化的时候出现一次，这就使得改变一个应用的具体工厂变得非常容易，它只需要改变具体工厂即可使用不同的产品配置，第二大好处是，它让具体的创建实例过程与客户端分离，客户端是通过它们的抽象接口操纵实例，产品的具体类名也被具体工厂的实现分离，不会出现在客户代码中，

缺点：抽象工厂模式可以很方便的切换两个数据库访问的代码，但如果你的需求来自增加功能，如增加项目表Project，需要改动哪些部分？至少增加三个类，IProject，SqlserverProject，AccessProject，需更改三个类，IFactory，SqlserverFactory，AccessFactory，并且客户端程序显然不会只有一个，如果有100个调用数据库访问的类，是不是要更改100次 IFactory factory = new AccessFactory( ); 这样的代码才行呢？这不能解决我要更改数据库时，改动一处就完全更改的要求阿，

15.7 用简单工厂来改进抽象工厂

namespace 抽象工厂模式
{
    class Program
    {
        static void Main(string[] args)
        {
            User user = new User();
            Department dept = new Department();

            IUser iu = DataAccess.CreateUser();
            iu.Insert(user);
            iu.GetUser(1);

            IDepartment id = DataAccess.CreateDepartment();
            id.Insert(dept);
            id.GetDepartment(1);

            Console.Read();
        }
    }

    class User
    {
        private int _id;

        public int ID
        {
            get { return _id; }
            set { _id = value; }
        }

        private string _name;

        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }
    }

    class Department
    {
        private int _id;

        public int ID
        {
            get { return _id; }
            set { _id = value; }
        }

        private string _deptName;

        public string DeptName
        {
            get { return _deptName; }
            set { _deptName = value; }
        }
    }

    interface IUser
    {
        void Insert(User user);

        User GetUser(int id);
    }

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

        public User GetUser(int id)
        {
            Console.WriteLine("在Sqlserver中根据ID得到User表一条记录");
            return null;
        }
    }

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

        public User GetUser(int id)
        {
            Console.WriteLine("在Access中根据ID得到User表一条记录");
            return null;
        }
    }

    interface IDepartment
    {
        void Insert(Department department);

        Department GetDepartment(int id);
    }

    class SqlserverDepartment : IDepartment
    {
        public void Insert(Department department)
        {
            Console.WriteLine("在Sqlserver中给Department表增加一条记录");
        }

        public Department GetDepartment(int id)
        {
            Console.WriteLine("在Sqlserver中根据ID得到Department表一条记录");
            return null;
        }
    }

    class AccessDepartment : IDepartment
    {
        public void Insert(Department department)
        {
            Console.WriteLine("在Access中给Department表增加一条记录");
        }

        public Department GetDepartment(int id)
        {
            Console.WriteLine("在Access中根据ID得到Department表一条记录");
            return null;
        }
    }

    class DataAccess
    {
        private static readonly string db = "Sqlserver";                    //与其用IFactory，SqlserverFactory，AccessFactory三个工厂类，
        //private static readonly string db = "Access";                     //不如直接用一个简单工厂来实现，DataAccess类取而代之它们，
                                                                            //客户端没有出现任何一个SQLServer或Access的字样，达到了解耦的目的，
        public static IUser CreateUser()                                    //客户端已经不在受改动数据库访问的影响了，
        {                                                                   //但增加数据库访问就麻烦了，
            IUser result = null;
            switch (db)
            {
                case "Sqlserver":
                    result = new SqlserverUser();
                    break;
                case "Access":
                    result = new AccessUser();
                    break;
            }
            return result;
        }

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

}

15.8 用反射+抽象工厂的数据访问程序

Assembly.Load("程序集名称").CreateInstance("命名空间.类名称");

原来实例化是写死在程序里的，现在用了反射就可以利用字符串来实例化对象，而变量是可以更换的，即变量"db"，

namespace 抽象工厂模式
{
    class Program
    {
        static void Main(string[] args)
        {
            User user = new User();
            Department dept = new Department();

            IUser iu = DataAccess.CreateUser();
            iu.Insert(user);
            iu.GetUser(1);

            IDepartment id = DataAccess.CreateDepartment();
            id.Insert(dept);
            id.GetDepartment(1);

            Console.Read();
        }
    }

    class User
    {
        private int _id;

        public int ID
        {
            get { return _id; }
            set { _id = value; }
        }

        private string _name;

        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }
    }

    class Department
    {
        private int _id;

        public int ID
        {
            get { return _id; }
            set { _id = value; }
        }

        private string _deptName;

        public string DeptName
        {
            get { return _deptName; }
            set { _deptName = value; }
        }
    }

    interface IUser
    {
        void Insert(User user);

        User GetUser(int id);
    }

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

        public User GetUser(int id)
        {
            Console.WriteLine("在Sqlserver中根据ID得到User表一条记录");
            return null;
        }
    }

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

        public User GetUser(int id)
        {
            Console.WriteLine("在Access中根据ID得到User表一条记录");
            return null;
        }
    }

    interface IDepartment
    {
        void Insert(Department department);

        Department GetDepartment(int id);
    }

    class SqlserverDepartment : IDepartment
    {
        public void Insert(Department department)
        {
            Console.WriteLine("在Sqlserver中给Department表增加一条记录");
        }

        public Department GetDepartment(int id)
        {
            Console.WriteLine("在Sqlserver中根据ID得到Department表一条记录");
            return null;
        }
    }

    class AccessDepartment : IDepartment
    {
        public void Insert(Department department)
        {
            Console.WriteLine("在Access中给Department表增加一条记录");
        }

        public Department GetDepartment(int id)
        {
            Console.WriteLine("在Access中根据ID得到Department表一条记录");
            return null;
        }
    }

    class DataAccess
    {
        //程序集名称，
        private static readonly string AssemblyName = "抽象工厂模式";

        //数据库名称，
        private static readonly string db = "Sqlserver";
        //private static readonly string db = "Access";

        public static IUser CreateUser()
        {
            string className = AssemblyName + "." + db + "User";                  //此处是字符串，可以用变量来处理，也就可以根据需要更换，
            return (IUser)Assembly.Load(AssemblyName).CreateInstance(className);
        }

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

}

 

15.9 用反射+配置文件的数据访问程序

namespace 抽象工厂模式
{
    class Program
    {
        static void Main(string[] args)
        {
            User user = new User();
            Department dept = new Department();

            IUser iu = DataAccess.CreateUser();
            iu.Insert(user);
            iu.GetUser(1);

            IDepartment id = DataAccess.CreateDepartment();
            id.Insert(dept);
            id.GetDepartment(1);

            Console.Read();
        }
    }

    class User
    {
        private int _id;

        public int ID
        {
            get { return _id; }
            set { _id = value; }
        }

        private string _name;

        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }
    }

    class Department
    {
        private int _id;

        public int ID
        {
            get { return _id; }
            set { _id = value; }
        }

        private string _deptName;

        public string DeptName
        {
            get { return _deptName; }
            set { _deptName = value; }
        }
    }

    interface IUser
    {
        void Insert(User user);

        User GetUser(int id);
    }

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

        public User GetUser(int id)
        {
            Console.WriteLine("在Sqlserver中根据ID得到User表一条记录");
            return null;
        }
    }

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

        public User GetUser(int id)
        {
            Console.WriteLine("在Access中根据ID得到User表一条记录");
            return null;
        }
    }

    interface IDepartment
    {
        void Insert(Department department);

        Department GetDepartment(int id);
    }

    class SqlserverDepartment : IDepartment
    {
        public void Insert(Department department)
        {
            Console.WriteLine("在Sqlserver中给Department表增加一条记录");
        }

        public Department GetDepartment(int id)
        {
            Console.WriteLine("在Sqlserver中根据ID得到Department表一条记录");
            return null;
        }
    }

    class AccessDepartment : IDepartment
    {
        public void Insert(Department department)
        {
            Console.WriteLine("在Access中给Department表增加一条记录");
        }

        public Department GetDepartment(int id)
        {
            Console.WriteLine("在Access中根据ID得到Department表一条记录");
            return null;
        }
    }

    class DataAccess
    {
        private static readonly string AssemblyName = "抽象工厂模式";

        //读配置文件，
        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);
        }
    }

}

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <appSettings>
        <add key="DB" value="Access"/>
    </appSettings>
</configuration>

15.10 无痴迷 不成功