GitHub User: nicholasjhenry
When unit testing the Service Object I can easily stub the method find_by_username. However the where would required an ugly stub chain. If the API changes the where clause is more costly than the find_by_username.
Having said that, there maybe a day when find_by_username is deprecated like it's cousin, find_all_by_ in Rails 4 and I would regret that choice :-)
If working on a team and they wanted to move the method find_by_username to the User I would be be totally cool with that, perhaps using the ActiveRelation syntax to build the query.
I know some folks advocate even hide the all method within their model, for example:
alias_method :all_posts, :all
Anyway, I hope that gives you some idea into my thought process behind that :-)
Thank you for highlighting the use of Service Objects, it's a technique that I have adopted and felt has improved the codebase for the projects I have worked on. There's probably one piece of code I would push back down into the model:
This query method exposes the ActiveRecord Query API and I would rather have that encapsulated in the ActiveRecord model. find_by_username is debatable, but I typically let those slip.