Question

In our current project, for some operations we send messages to Database like COMPLETED-Order,STARTED-Request, REJECTED-Order with related information like OrderId…. All the messages correspond a Command class that implements Command Pattern.

interface ICommand
{
   void Execute();
}

public class RequestStartedCommand:ICommand
{
   public void Execute()
   {
     //do the related work.....
   }
}

//other commands...

A windows service consumes this messages then converts them above commands and executes commands by a ThreadPool.

But some commands needed to be executed before other commands like OrderID=23’s COMPLETED-Order command must be executed before same order’s REJECTED-Order command. How can I do this or Which strategy should I follow? Any examples or documentation would be usefull.

Answer 1

I would try to implement some dependency check. Something like that rejected order command needs to check for some state to be valid before it can be executed.
The manager/service shoudl take the command from the list, apply its validation check and return it to the list if such a validation is not complete.

Beware of starvation, or for a command to get stuck in the list forever.