第十五章-抽象工厂模式

抽象工厂模式(Abstract Factory): 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。

IFactory是一个抽象工厂接口，它里面应该包含所有的产品创建的抽象方法。而ConcreteFactory1和ConcreteFactory2就是具体的工厂了。
通常是在运行时刻在创建一个ConcreteFactory类的实例，这个具体的工厂再创建具有特定实现的产品对象，也就是说，为创建不同的产品对象，客户端应使用不同的具体工厂。

#include<iostream>
#include<string>
#include<vector>

using namespace std;

class User {};
class Department {};

class IUser
{
public:
	virtual void Insert(User* user) = 0;
	virtual User* GetUser(int id) = 0;
};

class SqlserverUser :public IUser
{
public:
	void Insert(User* user)
	{
		cout << "在SQL Server中给User表增加一条记录" << endl;
	}

	User* GetUser(int id)
	{
		cout << "在SQL Server中根据ID得到User表一条记录" << endl;
		return nullptr;
	}
};

class AccessUser :public IUser
{
public:
	void Insert(User* user)
	{
		cout << "在Access中给User表增加一条记录" << endl;
	}

	User* GetUser(int id)
	{
		cout << "在Access中根据ID得到User表一条记录" << endl;
		return nullptr;
	}
};

class IDepartment
{
public:
	virtual void Insert(Department* department) = 0;
	virtual Department* GetDeparment(int id) = 0;
};

class SqlserverDepartment :public IDepartment
{
public:
	void Insert(Department* department)
	{
		cout << "在SQL Server中给Department表增加一条记录" << endl;
	}

	Department* GetDeparment(int id)
	{
		cout << "在SQL Server中根据ID得到Department表一条记录" << endl;
		return nullptr;
	}
};

class AccessDepartment :public IDepartment
{
public:
	void Insert(Department* department)
	{
		cout << "在Access中给Department表增加一条记录" << endl;
	}

	Department* GetDeparment(int id)
	{
		cout << "在Access中根据ID得到Department表一条记录" << endl;
		return nullptr;
	}
};

class IFactory
{
public:
	virtual IUser* CreateUser() = 0;

	virtual IDepartment* CreateDepartment() = 0;
};

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

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

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

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


int main()
{
	User* user = new User();
	Department* dept = new Department();

	IFactory* factory = new SqlServerFactory();

	IUser* iu = factory->CreateUser();

	iu->Insert(user);
	iu->GetUser(1);

	IDepartment* id = factory->CreateDepartment();
	id->Insert(dept);
	id->GetDeparment(1);



	system("pause");
	return 0;
}

• 优点：一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，他只需要改变具体工厂即可使用不同的产品配置。再一点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: 当需要增加需求是，比如添加一个Oracle数据库是，需要进行大批量的改动。

用简单工厂来改进抽象工厂

#include<iostream>
#include<string>
#include<vector>

using namespace std;

class User {};
class Department {};

class IUser
{
public:
	virtual void Insert(User* user) = 0;
	virtual User* GetUser(int id) = 0;
};

class SqlserverUser :public IUser
{
public:
	void Insert(User* user)
	{
		cout << "在SQL Server中给User表增加一条记录" << endl;
	}

	User* GetUser(int id)
	{
		cout << "在SQL Server中根据ID得到User表一条记录" << endl;
		return nullptr;
	}
};

class AccessUser :public IUser
{
public:
	void Insert(User* user)
	{
		cout << "在Access中给User表增加一条记录" << endl;
	}

	User* GetUser(int id)
	{
		cout << "在Access中根据ID得到User表一条记录" << endl;
		return nullptr;
	}
};

class IDepartment
{
public:
	virtual void Insert(Department* department) = 0;
	virtual Department* GetDeparment(int id) = 0;
};

class SqlserverDepartment :public IDepartment
{
public:
	void Insert(Department* department)
	{
		cout << "在SQL Server中给Department表增加一条记录" << endl;
	}

	Department* GetDeparment(int id)
	{
		cout << "在SQL Server中根据ID得到Department表一条记录" << endl;
		return nullptr;
	}
};

class AccessDepartment :public IDepartment
{
public:
	void Insert(Department* department)
	{
		cout << "在Access中给Department表增加一条记录" << endl;
	}

	Department* GetDeparment(int id)
	{
		cout << "在Access中根据ID得到Department表一条记录" << endl;
		return nullptr;
	}
};

class DataAccess
{
private:
	static const string db;
public:
	static IUser* CreateUser()
	{
		IUser* result = nullptr;
		if (db == "Sqlserver")
		{
			result = new SqlserverUser();
		}
		else if (db == "Access")
		{
			result = new AccessUser();
		}

		return result;
	}

	static IDepartment* CreateDepartment()
	{
		IDepartment* result = nullptr;
		if (db == "Sqlserver")
		{
			result = new SqlserverDepartment();
		}
		else if (db == "Access")
		{
			result = new AccessDepartment();
		}

		return result;
	}

};
const string DataAccess::db = "Sqlserver";


int main()
{
	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->GetDeparment(1);


	system("pause");
	return 0;
}

用反射+抽象工厂
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