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Asked: 2026-05-28T03:47:35+00:00

I’m trying to wrap my head around CQRS (Command Query Response Separation) per Martin

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I’m trying to wrap my head around CQRS (Command Query Response Separation) per Martin Fowlers recent post at:

http://martinfowler.com/bliki/CQRS.html

Given a project:

Main Database (Postgres):
  Product has many Sales
  User has many Sales

Reporting Database (NoSQL - Mongodb)
  Transaction (A Product and a Sale and a User)

And a requirement of producing a chart of transaction dollars per day for a given month.

  • What controllers would I need for reporting?
    • A Reports controller for views and partials
    • A Graphs controller for pulling the specific info for a graph out of the Reporting DB?
  • What the heck would the DTO (Data-Transfer Object) be in this case?
  • Is this really CQRS?
    • I assume so, since Reports/Graphs created from reporting DB would not be changing state, just a view on the main DB?

Thanks!

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  1. Editorial Team

    If you’re still interested in investigating CQRS with Rails have a look at rcqrs a Ruby CQRS with Event Sourcing library I created.

    There’s also a Rails 3 plugin to integrate with your Rails app that comes with generators to ease common tasks for creating commands, events and controllers using the CQRS pattern.

    Finally, there is a very simple sample blog Rails application to look at how you might use CQRS with Rails (look at my GitHub account for more details).

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