Skip to main content

Ruby and CQRS - Command methods should return nothing

CQRS stands for Command Query Responsibility Segregation and the basic rules are:
Commands - Perform (side effects) actions on the system and don't return values.
Queries  - Return values but can't touch the system's state.
Idealy, you don't mix them. Hence you can say, commands are dangerous, and
queries are safe.

Now, ruby doesn't have a specific type to say: this method (command) returns nothing, like void in C and other languages. So, the question is: How do you state that a particular method returns nothing?

Based on comments from the ruby mailing list, people are using these approaches;
1. Return self.
2. Return nil.
3. Implicit return (which in general, ends up being nil).

If I'd have to pick one, I'd go with the last one, but I also like to throw
another option into the mix....
Why don't create a class for this particular use case? Let's say, Nothing!

module Nothing
class Nothing
end

def nothing
@nothing ||= Nothing.new
end
end

class CommandQueryApi
include Nothing

# By using the nothing helper, is clear that the method returns, nothing!
def cmd_foo
# Do something
nothing
end
end


I 've used this approach a couple of times, and at least to me and my team, when you look at the code, is pretty clear that the method returns, well, nothing ;)

Not sure is this is the ruby way, but has being working so far.

Comments

  1. Nice article, thanks for the information. You give me some idea's. I will bookmark for next reference.


    Learn more Cloud Contact Centers

    ReplyDelete
  2. Wow interesting! !!first i was read this article i was amaze,hope many readers you may help.. Goodluck!!


    Horseshoe Bay Real Estate

    ReplyDelete
  3. Thanks for sharing wonderful information of giving best information. Its more useful and more helpful. Great doing keep sharing.

    wait till you see Shoretel Resellers

    ReplyDelete
  4. Just got an idea. Very helpful post.

    ReplyDelete

Post a Comment

Popular posts from this blog

Moving to Medium

It's been a long time since I want to give medium a try, and finally, I made some time to do it. To get started on the new platform, I'll be doing series on "Getting programming concepts, languages and tools". If it sounds interesting to you, please take a look at the first post  Getting AWK  and spread the word if you like it. I'm not going to migrate old entries to the new web site. They will remain here safe and sound! As usual, thanks for reading!

Working with unattended reports

In this post I‘ll show you how to create reports that NRapid will execute into an unattended mode. I strongly recommend using this kind of reports in automation scenarios only , and let the user see the print preview dialog in the rest of cases. The only difference between this reports and the standard ones, is that you will cannot make use of dialogs, the runtime will always pass in empty views to the ConfigureReport method. The ConfigureReport method will be executed, but you will have to grab the arguments from somewhere else. The execution pipeline is the same that NRapid uses for standard reports. This is the code to print out the whole list of categories in a dialogless mode. Notice that this report inherits from UnattendedReport class, this class tells to NRapid “run the report unattended”. Also notice that this class comes with a convenience method to configure the report with no arguments. You still can override the one that gets the view data but you will always

How to show excel files inside the .NET Webbrowser Control

If you are reading this, chances are you been banging your head against the wall for a couple of hours (or even days) trying to show excel files inside the WinForms webbrowser control. Possible reasons you ended up in here: You had working code that got broke after upgrading from Win 7. Your code doesn’t work the same way between machines running different (newer) versions of IE. A download box pops up every time your app tries to show an excel file inside the webbrowser control (you wanna show the actual content). You just have no clue on how to get excel working into the .NET embedded webbrowser control. You are trying to implement IInternetSecurityManager and don’t know where to start. (Or how don’t know how to delegate calls to your security manager). Among many other, maybe….. Yes, COM is a PITA, so is ActiveX and IE (Embedded or full for that matter). And no, showing excel files inside the webbrowser control shouldn’t be that hard, but sometimes we have