How does OOP translate to Rails? - ruby-on-rails

Question

I'm having a hard time wrapping my head around Rails' MVC system and its relationship to Ruby classes. In Rails, it feels like objects go out the window and are replaced by databases.
I'm working on an interview question right now and it requires me to create a website that accepts HTTP requests and returns responses. I'm not super familiar with JS and I like Ruby a lot so I've been using Rails. But I feel so limited by the database... it feels like things that I could do so easily in Ruby (e.g., look through a hash of objects and filter by multiple constraints until I got what I wanted) are so much more difficult with a database.
The interview question says I don't need to use a durable data store, but that seems like a big no-no in Rails. Does anyone have advice for how to change my mindset around this? (Or, in the short term, recommendations for other easy-to-use tools?)
BTW - I know this may beg the question, "why are you interviewing if you don't know this stuff?" It's an internship and I'm just trying to start interviewing as much as possible so I get used to the process.

Answer 1

But I feel so limited by the database... it feels like things that I could do so easily in Ruby (e.g., look through a hash of objects and filter by multiple constraints until I got what I wanted) are so much more difficult with a database.
Working with databases is challenging since SQL is a completely different paradigm. Instead of being object oriented SQL is based on tables and relational algebra.
Everyone finds it easier to hack out loops and create if/else constructs to munge data as a beginner. But its not really a viable solution at scale. Any time you spend learning SQL will pay off immensely in the future.
I'm having a hard time wrapping my head around Rails' MVC system and its relationship to Ruby classes. In Rails, it feels like objects go out the window and are replaced by databases.
This doesn't really have that much do with Rails or MVC. Its rather ActiveRecord which is the object relational mapper (ORM) which is built into Rails by default.
In comparison with other ORM's ActiveRecord has a lot of magic. It reads your table definitions from the database and automatically sets up attributes - in other ORMs you do this explicitly in your model classes, a repository class, XML files or annotations. This magic is great for productivity but can be very difficult to wrap your head around as a beginner.
ActiveRecord is still very much an object oriented design - just with more metaprogramming then you may be used to.
The interview question says I don't need to use a durable data store,
but that seems like a big no-no in Rails.
This is a misconception. Rails is a very modular framework and can be used without ActiveRecord, with other object relational mappers (or object-document mappers) or even without any storage at all.
Models are also are not necissarily even persisted at all. They are just objects that encompass the buisness logic of your application.
Most beginner guides start with ActiveRecord as an overwhelming majority web applications use a SQL database*.

Answer 2

I agree that this is probably one of the hardest things newbies face in Rails. In the Rails guide, models are almost always Active Record models (aka map to a database table). However, it's totally normal that not all of your models are Active Record models and / or need to be persisted. I think the term you're missing are Plain Old Ruby Objects (PORO) and Active Model.
A PORO could be anything from something super simple, a mapping to an API or composing several other (ActiveRecords) models together.
For example, you could have a versions controller which displays the latest version of your web app. The version would be determined by reading the SHA from the git repository, file or env variable. So it would never be persisted in the database.
class Version
def self.from_git
new(`git rev-parse HEAD`)
end
def initialize(name)
#name = name
end
def to_s
#name
end
end
class VersionsController
def show
#version = Version.from_git
end
end
Here are some links you might find useful
https://www.codewithjason.com/code-without-service-objects/
https://www.oreilly.com/library/view/build-chatbot-interactions/9781680507089/f_0047.xhtml
https://thecodest.co/blog/hi-im-poro-2/
https://www.toptal.com/ruby-on-rails/decoupling-rails-components
https://guides.rubyonrails.org/active_model_basics.html
https://www.codewithjason.com/extracting-tidy-poro-messy-active-record-model/