Written by Matthew Mayer
on April 13, 2021

Tiny guide to Rails

The tiny guide to Rails (that I wish I had)

I’ve found Rails to rely on more convention over configuration than I’m comfortable with - so much so it seemed impenetrable at times. This is the tiny guide to Rails I wish I had to understand where code lives and how the application works.

Know where to find things

Go to definition or go to implementation doesn’t work well with Rails projects and most IDEs I’ve tried. It’s important to know where to find code:

Controllers: app/controllers/foo_controller.rb
Views: app/views/foo/bar.html.erb. Controller app/controllers/foo_controller.rb above maps to app/views/foo/ and the controller’s function bar finds the bar.html.erb file
Models: app/models/item_foo.rb

Models

Naming: an ActiveRecord model with a declaration like class ImportFile < ApplicationRecord will be accessed like ImportFile.create but the file must be named import_file.rb.
Plurals: if a model called Widget has many ImportFile models from above, they will be accessed like so: Widget.find(widget_id).import_files.
Fields can be accessed by .field_name. For the ImportFile class above, if we find an item with ImportFile.find(import_id) we can access the filename field like so: ImportFile.find(import_id).filename. If the field does not exist in the database an error occurs at runtime.
Lots of validators and attributes etc… are available for Models. Every addition made to the Model file can increase complexity for the next person.
Schema reference: located in db/schema.rb. This contains most but not all fields available. For example an ID field is in the database but not the schema file. Keep this file up to date for easy reference of field names.

Controller and View communication

Controllers set instance variables (@foo) which are available in the View.

Controller:

def show
  @foo = ImportFile.find(import_id)
end

View:

<h1>foo filename is <%= @foo.filename %></h1>

If the view tries to access a variable or a field on the variable that doesn’t exist an error occurs at runtime.

Views

Two syntaxes are available in .erb files.

<%= RUBY CODE RETURNING A STRING => will evaluate the items in the Ruby code block and return the contents.

<% RUBY CODE %> will evaluate the contents but not insert the value into the rendered page. This is useful for if/else statements:

<% if @foo.bar.nil? %>
  <p>❌</p> 
<% else %>
  <p>✅</p> 
<% end %>

Resources

https://guides.rubyonrails.org/

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