Ruby/Rails Cheat Sheet

In Rails, there are different conventions for the:

  1. File name (outside) e.g. orders_controller.rb

  2. File definition (inside) e.g. OrdersController

  3. File location (inside) e.g. /app/controllers

Rails Naming Convention

Rails use the same naming convention as Ruby (for a list of the Ruby naming conventions scroll down) with some additions:

Variable - order_amount total Variables are named where all letters are lowercase and words are separated by underscores.

Class and Module - InvoiceItem Classes and modules use MixedCase and have no underscores, each word starts with a uppercase letter.

Database Table - invoice_items orders Table names have all lowercase letters and underscores between words, also all table names need to be plural.

Model - Order The model is named using the class naming convention of unbroken MixedCase and is always the singular of the table name. e.g.

  • Table name might be orders (plural)

  • The model name would be Order (singular)

  • Rails will then look for the class definition in a file called order.rb in the /app/models directory.

  • If the model class name has multiple capitalised words, the table name is assumed to have underscores between these words.

Controller - OrdersController Controller class names are pluralized, such that OrdersController would be the controller class for the orders table. Rails will then look for the class definition in a file called orders_controller.rb in the /app/controllers directory.

Files, Directories and other pluralization Files are named using lowercase and underscores. Assuming we have an Orders controller then the following other conventions will apply:

  • That there is a helper module named OrdersHelper in the orders_helper.rb found in the app/helpers directory.

  • Rails will look for view template files for the controller in the app/views/orders directory.

  • Output from this view will then be used in the layout defined in the orders.html.erb in the app/views/layouts directory.

  • Test files including order_test.rb will be created in the /test/unit directory, a file will be created in the /test/fixturesdirectory called orders.yml and finally a file called orders_controller_test.rb will be created in the /test/functional directory

Primary Key The primary key of a table is assumed to be named id.

Foreign Key The foreign key is named with the singular version of the target table name with _id appended to it, e.g. order_id in the items table where we have items linked to the orders table.

Many to Many Link Tables Tables used to join two tables in a many to many relationship is named using the table names they link, with the table names in alphabetical order, for example items_orders.

Automated Record Timestamps You can get ActiveRecord to automatically update the create and update times of records in a database table. To do this create two specially named columns created_at and updated_at to your table, i.e. t.datetime :created_at and t.datetime :updated_at. If you only want to store the date rather than a date and time, use :created_on and :updated_on.

Naming Convention Summary

Model Naming Convention

Table: 			orders
Class: 			Order
File: 			/app/models/order.rb
Primary Key: 	id
Foreign Key: 	customer_id
Link Tables: 	items_orders

Controller Naming Convention

Class: 			OrdersController
File: 			/app/controllers/orders_controller.rb
Layout: 		/app/layouts/orders.html.erb

View Naming Convention

Helper: 		/app/helpers/orders_helper.rb
Helper Module: 	OrdersHelper
Views: 			/app/views/orders/… (list.html.erb for example)

Tests Naming Convention

Unit: 			/test/unit/order_test.rb
Functional: 	/test/functional/orders_controller_test.rb
Fixtures: 		/test/fixtures/orders.yml

The Ruby Naming Conventions

As Jon would say, ProTip:

Ruby uses the first character of the name to help it determine it’s intended use.

Global Variables

Starts with a dollar ($) sign followed by other characters

$age = 21
$name = "Joseph"

Local Variables

These should be a lowercase letter followed by other characters, naming convention states that it is better to use underscores rather than camelBack for multiple word names

_age = 21
_name = "Joseph"

Instance Variables

Instance variables are defined using the single "at" sign (@) followed by a name. It is suggested that a lowercase letter should be used after the @

@age = 21


Constant names start with an uppercase letter followed by other characters. Constant objects are by convention named using all uppercase letters and underscores between words

AGE = 21 # constant; by convention - constants can be modified and generate a warning

Class Variables

Class variable names start with a double "at" sign (@@) and may be followed by digits, underscores, and letters.

class Car
    @@wheels = 4

    def initialize(make)
        @make = make

    def self.wheels
    attr_accessor :make

#outside the class
civic ="Honda")

#instance variable, called on the object
>> civic.make
=> "Honda"
#class variable, called on the class itself
>> Car.wheels
=> 4

Instance Methods

Instance Methods can only be called on a particular instance of the class. You use Instance Methods when you need to act on a particular instance of the class. This is often when the functionality concerns the identity of the instance such as calling properties on the object, or invoking behavior.

class Basket  
  def self.find(id)  
    puts "finding basket with the id of #{id}"  

  def products  

# in the rails console
basket =  
=> #<Basket:0x007fd2e446c7b0>

=> []  

Class Method

A Class Method is a method that is defined on the class. In this example I’ve defined a find method on the Basket class that accepts an id. You should use Class Methods when the functionality you are writing does not belong to an instance of that class.

class Basket  
  def self.find(id) # self signifies that this method is a Class Method. 
    puts "finding basket with the id of #{id}"  

# to use this method
basket = Basket.find(‘abc’)  


A function is a block of code that can be called from another location in the program or class. It is used to reduce the repetition of multiple lines of code. A function can either return nil, a value, or an array of values. If multiple items are returned, they will be returned as an array.

# Syntax
# standard functions
# if within a class, called on the object
def functionName(passedParameters)

   # code to be executed

   # optional return value or variable
   return value
   # another way to return value
# Example
def absolute_value(x)
    if x < 0
        x = x * -1
    return x


A block contains code that can be executed. Blocks are not objects, but there are methods that can be used on blocks for repetition and local variable purposes.

# Syntax
# x is a local variable which represents a parameter passed into a block
# one way to write a block
{ |x|
    # code to be executed

# other way to do it
do |x|
    # code to be executed
# Example
10.times { puts "This code will execute 10 times!" }


Applies a block onto every item in an array. Collect does not modify an array, rather it returns a copy.

# Syntax
array.collect { |element| #code to run on element }
# Example
numberLine = [ 1, 2, 3, 4, 5 ]
shiftedNumberLine = numberLine.collect { |number| number + 1 }

# Output =>
shiftedNumberLine is [2, 3, 4, 5, 6]

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