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

Migrating an ASP.NET MVC 4 app from Azure websites to WinHost

About a week ago I've to migrate an ASP.NET MVC 4/EF5 application from Azure websites to WinHost. While the process was really smooth, there were some caveats related to database connections that I want to share with you. Create and setup the ftp profile on VS and configure the connection string was really easy, WinHost provide you those values and there is nothing special here. But once you deploy your website and try to see it online, you may get the “yellow screen of dead” with the message: "A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)" Assuming you wrote the connection string properly, this happens because you cannot use the default connection name in your web.c

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

How to replace text with images on Word documents using C#

This post it’s a reply to a question I got from a previous post that shows how to work with Word templates from C# code . If you haven’t read it, I recommend to do so because I’m not going into details here. But basically it was about how to create a Word document from a template and perform same text manipulation. So, the question from Marcel Kieboom  was “Do you know if it would be also possible to replace one of the words with an image which is locally stored?” The answer is yes, and this is how you can do that. Based on the same convention I had used in the previous post, I should have a template like this: What I’m trying to do here is replace the text [angus-young] for an actual pic of Angus. The technique I’m using it’s pretty common on web sites and basically consist in have an image with a matching name for each keyword I want to replace and then create the image path dynamically. This is the C# code to do that. * When I execute the f