工厂模式和对象持久化

Question

我在我的应用程序的一个部分中使用工厂设计模式，我注意到使用常规工厂模式每次都会创建一个新对象。我有一个场景，我需要多次迭代工厂 class 中的 createinstance 方法，并且每次都会创建一个新的消费者对象。

在 Program.cs 中，我创建了人员列表，我在其中键入了一些随机输入数据。基于对每个人的操作的代码应该动态执行class中的流程方法。这个逻辑似乎按我的预期工作，但如果重复相同的操作，则会多次创建相同的对象。

为了解决这个问题，我修改了 ActionFactory class（在下面修改后的 Action Factory 片段中显示），我在其中维护一个字典来保存为特定操作创建的实例。如果重复该操作，那么我不会创建新实例，而是从字典中获取先前创建的实例。这似乎解决了 Output2 图像中所示的问题。

但是如果我在 "Modified Action Factory" class 中所做的就足够了（或者）我是否应该使用任何其他模式而不是 Factory，我想从专业人士那里得到 know/learn此类问题的设计模式。为了维护单个对象，我能想到的另一种方法可能是在每个 Action classes 中创建一个单例对象，但问题是我如何从工厂调用单例实例 class??由于工厂 class 总是调用 createinstance 而不会调用单例实例。我是设计模式的新手，我很高兴能更多地了解它们并提高我的编码标准。提前致谢

代码如下：

  class Program
{
    static void Main(string[] args)
    {
        List<Person> ListofPeople = new List<Person>();

        Person p1 = new Person() {Name = "P1", State = "CA", Action = "Add"};

        ListofPeople.Add(p1);

        Person p2 = new Person() { Name = "P2", State = "NJ", Action = "Add" };

        ListofPeople.Add(p2);

        Person p3 = new Person() { Name = "P3", State = "VA", Action = "Update" };

        ListofPeople.Add(p3);

        Person p4 = new Person() { Name = "P4", State = "VA", Action = "Update" };

        ListofPeople.Add(p4);


        Person p5 = new Person() { Name = "P5", State = "VA", Action = "Update" };

        ListofPeople.Add(p5);


        Person p6 = new Person() { Name = "P6", State = "VA", Action = "Delete" };

        ListofPeople.Add(p6);


        ActionFactory factory= new ActionFactory();

        foreach (var person in ListofPeople)
        {
            IAction action = (IAction) factory.CreateInstance(person.Action.ToLower());

            action.Process();

        }
        Console.ReadKey();


    }
}

public class Person
{
    public string Name { get; set; }
    public string State { get; set; }
    public string Action { get; set; }

}

动作工厂：

public class ActionFactory
{
    Dictionary<string, Type> actions;

    public ActionFactory()
    {
        LoadTypesICanReturn();
    }

    public object CreateInstance(string actionName)
    {
        Type t = GetTypeToCreate(actionName);

        if (t == null)
            return null;

        var actionProcessor = Activator.CreateInstance(t) as IAction;

        return actionProcessor;
    }

    Type GetTypeToCreate(string actionName)
    {
        foreach (var action in actions)
        {
            if (action.Key.Contains(actionName))
            {
                return actions[action.Key];
            }
        }

        return null;
    }

    void LoadTypesICanReturn()
    {
        actions = new Dictionary<string, Type>();

        Type[] typesInThisAssembly = Assembly.GetExecutingAssembly().GetTypes();

        foreach (Type type in typesInThisAssembly)
        {
            if (type.GetInterface(typeof(IAction).ToString()) != null)
            {
                actions.Add(type.Name.ToLower(), type);
            }
        }
    }
}

IAction：

   public interface IAction
{
    void Process();
}

Add.cs

  public class Add: IAction
{

    public Add()
    {
        Console.WriteLine("add constructor...");
    }

    #region IAction Members

    public void Process()
    {
        Console.WriteLine("Add Processor....");
    }

    #endregion
}

Update.cs

 public class Update: IAction
{
    public Update()
    {
        Console.WriteLine("Update constructor...");
    }


    public void Process()
    {
        Console.WriteLine("Update Processor...");
    }
}

Delete.cs

public class Delete : IAction
{

    public Delete()
    {
        Console.WriteLine("Delete Constructor...");
    }



    #region IAction Members

    public void Process()
    {
        Console.WriteLine("Delete Processor...");
    }

    #endregion
}

控制台输出显示 IAction 消费者 classes 被实例化的次数

输出：

修改后的动作工厂：

 public class ActionFactory
{
    Dictionary<string, Type> actions;

    private Dictionary<Type, IAction> actionInstances; 

    public ActionFactory()
    {

        actionInstances = new Dictionary<Type, IAction>();
        LoadTypesICanReturn();
    }

    public object CreateInstance(string actionName)
    {
        Type t = GetTypeToCreate(actionName);

        if (t == null)
            return null;

        if (actionInstances.ContainsKey(t))

            return actionInstances[t];

        else
        {
            var actionProcessor = Activator.CreateInstance(t) as IAction;

            LoadIAction(t, actionProcessor);

            return actionProcessor;
        }


    }


    private void LoadIAction(Type t, IAction actionProcessor)
    {

        if (!actionInstances.ContainsKey(t))
        {
            actionInstances.Add(t, actionProcessor);
        }
    }

    Type GetTypeToCreate(string actionName)
    {
        foreach (var action in actions)
        {
            if (action.Key.Contains(actionName))
            {
                return actions[action.Key];
            }
        }

        return null;
    }

    void LoadTypesICanReturn()
    {
        actions = new Dictionary<string, Type>();

        Type[] typesInThisAssembly = Assembly.GetExecutingAssembly().GetTypes();

        foreach (Type type in typesInThisAssembly)
        {
            if (type.GetInterface(typeof(IAction).ToString()) != null)
            {
                actions.Add(type.Name.ToLower(), type);
            }
        }
    }
}

修改动作工厂后的输出：

Answer 1

Factory 设计模式用于简化对象的创建，通常当您不知道要创建的类型时，它会在运行时提供。
有时，也可能是因为它们有依赖关系，而你想抽象依赖关系的创建，或者只是因为你想做一些事情。

在您的例子中，Add、Update 和 Delete 是通常由某些第 3 方调用的方法，而不是数据类型本身，如 [=19] 所指定=] 以上。

您的案件可以由 Command Design Pattern 处理。

假设您想要加载一堆命令（又名：Add Person X, Update Person Y, Delete Person Z），并且您想要缓冲它们以备将来使用。

abstract class PersonCommand
{
    Person Person { protected get; } // you can call this payload, or person, w/e

    PersonCommand(Person person)
    {
        Person = person;
    }

    public abstract void Apply(); // can be called Execute or Process as well, or w/e. problem domain.
}

然后，每个命令都有一个实现：

class AddCommand : PersonCommand
{
    AddCommand(Person person) : base(person) { }
    public override void Apply()
    {
        // send REST PUT request, add person to DB, whatever you want to do here.
    }
}

class UpdateCommand : PersonCommand
{
    UpdateCommand(Person person) : base(person) { }
    public override void Apply()
    {
        // send REST POST request, update person in DB, whatever you want to do here.
    }
}

class DeleteCommand : PersonCommand
{
    DeleteCommand(Person person) : base(person) { }
    public override void Apply()
    {
        // send REST DELETE request, remove person from DB, whatever you want to do here.
    }
}

有了这个，您可以进行以下操作：

var commandsToExecute = new List<PersonCommand>();

commandsToExecute.Add(new AddCommand(new Person { Name = "asd", State = "CA" }));

commandsToExecute.Add(new UpdateCommand(new Person { Name = "barry", State = "CA" }));

commandsToExecute.Add(new DeleteCommand(new Person { Name = "barry", State = "CA" }));

commandsToExecute.ForEach(cmd => cmd.Apply());

现在，这是您可以执行的操作的一个基本示例。也许，在某些情况下，Command 并不那么容易创建，例如，他们可能需要了解您的 REST 请求的服务端点。

为此，可以创建一个 CommandFactory，然后可以通过操作名称处理创建：

class CommandFactory
{
    private readonly Dictionary<string, Func<Person, PersonCommand>> creationFuncs;

    CommandFactory(string backendUrl)
    {
        creationFuncs = new Dictionary<string, Func<Command, Person>>();

        creationFuncs.Add("add", (person) => return new AddCommand(backendUrl, person));
        creationFuncs.Add("update", (person) => return new UpdateCommand(backendUrl, person));
        creationFuncs.Add("delete", (person) => return new DeleteCommand(backendUrl, person));
    }

    PersonCommand Create(string action, Person person)
    {
        // validation can be added here
        return creationFuncs[action](person);
    }
}

用法为：

var factory = new CommandFactory("http://localhost:4200/person/");

var commandsToExecute = new List<PersonCommand>();

commandsToExecute.Add(factory.Create("add", new Person { Name = "asd", State = "CA" }));

commandsToExecute.Add(factory.Create("update", new Person { Name = "barry", State = "CA" }));

commandsToExecute.Add(factory.Create("delete", new Person { Name = "barry", State = "CA" }));

commandsToExecute.ForEach(cmd => cmd.Apply());

万物皆有设计模式，您应该找到适合您需要的那个。

工厂模式和对象持久化

Factory Pattern and object persistence

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