Comments on: Cairngorm Patterns: Batch Commands

By: Steve Brownlee

Steve Brownlee — Thu, 19 Jan 2012 04:51:14 +0000

That’s rather obvious, Denzo.

By: Denzo

Denzo — Thu, 19 Jan 2012 04:39:07 +0000

This will not work with asynchronous commands.

By: Rajesh V

Rajesh V — Mon, 19 Apr 2010 21:02:54 +0000

Thanks for the prompt reply, Steve. I am not sure how I would be able to capture data returned by the command, executing currently, before passing it on to the next?

By: Steve Brownlee

Steve Brownlee — Mon, 19 Apr 2010 19:27:15 +0000

Yes, you can chain the commands. Create a ChainCommands class that takes an invoker (Event) as a constructor argument, and also an array of command classes.

Then create the following methods:
execute() – This starts the command execution process by calling executeCommand()
executeCommand() – Performs the execution of the each command in the array
executeNextCommand() – This increments the internal counter to keep track of which command you are executing, captures any data from the current execution, and then calls executeCommand() again, forming the loop.

By: Rajesh V

Rajesh V — Mon, 19 Apr 2010 19:13:37 +0000

Excellent article, Steve! I found it very useful. However, I had a question, a little tangential maybe. I have this scenario: I have several commands, each loading a set of table contents into an app from a SQLite DB. I want to batch these commands together during the app start. However, I need one or more of these commands to fire (not just execute, but provide information (respond immediately) to the next command through either result/fault). I was wondering how I could achieve that. I am using an async connection to the DB. Is it just that I use Sync connections or can something be done to listen to callbacks before executing the next command?

Thanks!

By: Amichai Lesser

Amichai Lesser — Fri, 01 May 2009 16:58:38 +0000

Nice post.
In the following post http://www.awholenewweb.com/?p=51 I share an example in which I extended the events and commands to support Undo operations. I also needed to find a good way to avoid the N event files 1 for each data point in my model but I solved it by making the value object update its own properties.
Your approach seems applicable for many other use cases, thanks for sharing.

By: Steve Brownlee

Steve Brownlee — Fri, 24 Apr 2009 14:59:27 +0000

@Karl: Yes, I did not like the implementation of SequenceCommand because, imo, it broke the basic purpose of the Command pattern. This keeps each Command independent and decoupled from any other logic in the system.

By: Karl Sigiscar

Karl Sigiscar — Fri, 24 Apr 2009 14:34:22 +0000

Very useful indeed. I previously used SequenceCommand and nextEvent but this requires to do something special in each command.

Your approach seems to not require any modification to commands.