Using team and factory design patterns to complete tasks in a queue

Question

I have a list of tasks queued in the database that I need to read from the database and execute them in parallel using streaming, and I have a list of command classes for each of these tasks that implement a common interface (command template) but when I get pending jobs from the database, I will need to create an instance of the correct command object for each job something like this (in the factory class)

ICommand command;
switch (jobCode)
{
  case "A":
     command = new CommandA();
     break;
  case "B":
     command = new CommandB();
     break;
  case "C":
     command = new CommandC();
     break;
}

command.Execute();

Is there a better way to create the correct command object without using the large switch statement as above? OR is there another template for doing jobs in the queue?

: ( ). .

public class CommandFactory
{
    private readonly IDictionary<string, Func<ICommand>> _commands;

    public CommandFactory()
    {
        _commands = new Dictionary<string, Func<ICommand>>
                        {
                            {"A", () => new CommandA()},
                            {"B", () => new CommandB()},
                            {"C", () => new CommandC()}
                        };
    }

    public ICommand GetCommand(string jobKey)
    {
        Func<ICommand> command;
        _commands.TryGetValue(jobKey.ToUpper(), out command);
        return command();
    }
}    

Client: 

        var factory = new CommandFactory();
        var command = factory.GetCommand(jobKey);
        command.Execute();

Answer 1

# Java. ICommand:

public interface ICommand
{
    void Execute();
}

. , , .NET( Java ). Action , :

public class Prog
{
    public Prog()
    {
        var factory = new CommandFactory();
        factory.Register("A", () => new A().DoA);            
        factory.Register("B", () => new B().DoB);
        factory.Register("C", DoStuff);

        factory.Execute("A");
    }

  public static void DoStuff()
    {
    }
}

public class CommandFactory
{
    private readonly IDictionary<string, Action> _commands;       

    public void Register(string commandName, Action action)
    {
    _commands.Add(commandName, action); 
    }

    public Action GetCommand(string commandName)
    {
        _commands[commandName];
    }

    public void Execute(string commandName)
    {
        GetCommand(commandName)();
    }
}
public class A
{
    public void DoA()
    {
    }
}

public class B
{
    public void DoB()
    {
    }
}

, :

public interface ICommand
{
    void Execute();
    void Undo();
}

- :

public class Command
{
    public Command(Action execute, Action undo)
    {
        Execute = execute;
        Undo = undo;
    }

    public Action Execute { get; protected set; }
    public Action Undo { get; protected set; }
}

(, )

public class Command 
{
    private readonly Action _execute;
    private readonly Action _undo;

    public Command(Action execute, Action undo)
    {
        _execute = execute;
        _undo = undo;
    }

    public void Execute()
    {
        _execute();
    }

    public void Undo()
    { 
        _undo();
    }
}

( ICommand, . , factory Command)

, . , -:

public class Prog2
{
    public Prog2()
    {
        var factory = new CommandFactory2();
        factory.Register("A", new Lazy<Command>(
            ()=>
                {
                    var a = new A();
                    return new Command(a.DoA, a.UndoA);
                }));

        factory.Register("B", new Lazy<Command>(
           () =>
           {
               var c = new B();
               return new Command(c.DoB, c.DoB);
           }));

        factory.Register("C", new Lazy<Command>(
            () => new Command(DoStuff, UndoStuff)));

        factory.Execute("A");
    }

    public static void DoStuff()
    {
    }

    public static void UndoStuff()
    {
    }
}

public class CommandFactory2
{
    private readonly IDictionary<string, Lazy<Command>> _commands;

    public void Register(string commandName, Lazy<Command> lazyCommand)
    {
        _commands.Add(commandName, lazyCommand);
    }

    public void Register(string commandName, Action execute, Action undo)
    {
        _commands.Add(commandName, new Lazy<Command>(() => new Command(execute, undo)));
    }

    public Command GetCommand(string commandName)
    {
        return _commands[commandName].Value;
    }

    public void Execute(string commandName)
    {
        GetCommand(commandName).Execute();
    }

    public void Undo(string commandName)
    {
        GetCommand(commandName).Undo();
    }
}


public class A
{
    public void DoA()
    {
    }

    public void UndoA()
    {
    }
}

public class B
{
    public void DoB()
    {
    }

    public void UndoB()
    {
    }
}

, , (Execute, Undo ..). , Execute Undo . , , .

Answer 2

Dictionary / ICommand. - :

public class CommandFactory
{
    private readonly Dictionary<string, ICommand> mCommands = new Dictionary<string,ICommand>(StringComparer.OrdinalIgnoreCase);

    public void RegisterCommand<TCommand>(string commandKey) where TCommand : ICommand, new()
    {
        // Instantiate the command
        ICommand command = new TCommand();

        // Add to the collection
        mCommands.Add(commandKey, command);
    }

    public void ExecuteCommand(string commandKey)
    {
        // See if the command exists
        ICommand command;
        if (!mCommands.TryGetValue(commandKey, out command))
        {
            // TODO: Handle invalid command key
        }

        // Execute the command
        command.Execute();
    }
}

, string - . , , .

, , - :

public class CommandDetails<T> where T : ICommand, new()
{
    private ICommand mCommand;

    public ICommand GetCommand()
    {
        if (/* Determine if the command has been instantiated */)
        {
            // Instantiate the command
            mCommand = new T();
        }

        return mCommand;
    }
}

public void ExecuteCommand(...)
{
    // See if the command exists
    CommandDetails details;
    // ...

    // Get the command
    // Note: If we haven't got the command yet, this will instantiate it for us.
    ICommand command = details.GetCommand();

    // ...
}

Answer 3

You could ask your work to provide her own ICommand:

interface IJob 
{
  ICommand Command { get; }
}

public class JobA : IJob
{
  private readonly ICommand _command = new CommandA();
  public ICommand Command { get { return _command; } }
}

Then, instead of including the job code, you can simply do:

job.Command.Execute();