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

Post a Comment

Popular posts from this blog

How to create MS Word documents from Office templates using C#

The OpenXML SDK allows you to do pretty much anything you want with office files such as Excel, Word, etc… While many people like this library, I found it complex, unintuitive and poorly documented, not to mention the awful xml format that uses under the hood to represent the documents, styles, etc. So I decided not to use it and build my own solution. If you, like me, don’t like that library, you will find in this post an alternative approach to build word documents from templates using c#.
A neat trick to work with Office is to use the macro recorder to understand how things work. The macro recorder allows you to start a macro, do something by hand, stop it, and then take a look at the generated VBA code. Once you do this, you are pretty much set.
This is how it looks the template I’am going to use.


Note: save the file as a Word template (.dotx)
This is the code to create Word documents from C#:

By running the code, you should get a document that looks like this.


Note that the font, forma…

Printing html using the embedded web browser control

In this post I’ll try to answer some questions about the web browser control and provide some workarounds for known issues involved in the printing process.
I'm assuming that you have some experience with the web browser control and basic knowledge of COM and hosting APIs. So I’m not going to cover those topics.
At the bottom of this page I’ve added the links to download a small library I wrote that takes care of printing HTML and a demo app so you can try it out without having to write any code by yourself.
Using the code The HtmlPrinter class will allow you to print html from an URL or just passing the html as string, you can also specify the title and the number of copies you want to print. The code may look something like this: Now that we know how to use the API let get answer some questions.
Why my app crashes when I try to print multiple copies of a page? Well, apparently when you send a lot of print commands to the web browser control, there is a lot of COM crap in between that l…

WinForms, paging the DataGridView the right way

I know this may sound like old history, but in the enterprise world there is still a lot of WinForms development. Just a couple of days ago, I had to implement a custom DataGridView capable to work over a butt load of data (100K+ records) and keep responses times acceptables.
I thought paging will be a good way to go, and as WinForms is pretty old nowadays, I supposed it will be easy to find a couple examples on the web.
While in fact I found examples, all of them were incompletes and/or they wouldn't perform well in real world apps... So I decided to roll my own component and post it online. Hopefully, someone else will find it useful ;).


The bread and butter of this solution relies on LINQ and deferred execution. As LINQ takes care of all complicated work, it was quite easy to implement.
This component also supports conditional format, sorting and some search capabilities, but in this post I will concentrate on paging only (I'll cover the rest of the features in future posts)…