Virtual Attributes in Ruby on Rails

Let’s play with getter and setter from Ruby

Let’s consider a case when you have a Product model with attributes from migration such as name, price and quantity. For some reason, you also need an additional title attribute or you just need to modify the name attribute and use it as title for either in Product form or just to display on the view page.

ex. Product model with migration attributes and virtual attribute

So let’s discuss what are the possible options to add such attributes to the model.

class Product
  def initialize(name, price, quantity)
   @name = name
   @price = price
   @quantity = quantity
  end
  # getter
  def title
   "Exlusive #{@name}"
  end
  # setter
  def title=(value)
   @title = value
  end
end
product = Product.new('Cookies', 1, 10)
p product.name                 # => "Cookies" 
p product.title                # => "Exclusive Cookies" 
product.title='Summer Shirt'
p product.title                # => "Summer Shirt"

In this way, we can get the title value by the getter method and also set the value by the setter method without even adding any additional migration. Use cases could vary as per the requirement such as virtual attribute full_name when migration attributes as first_name and last_name and many more.

Alternatively, we can perform the same operation using attr_accessor , attr_reader and attr_writer. Ruby actually lets you create virtual attributes this way, which keeps you from having to manually create getter and setter methods as given below,

attr_reader   :title # getter
attr_writer   :title # setter
attr_accessor :title # both getter and setter

So if we stick to our previous example then it can be modified as,

class Product
  attr_accessor :title
  def initialize(name, price, quantity)
   @name = name
   @price = price
   @quantity = quantity
   @title = "Exlusive #{@name}"
  end
end
product = Product.new('Cookies', 1, 10)
p product.name                 # => "Cookies" 
p product.title                # => "Exclusive Cookies" 
product.title='Summer Shirt'
p product.title                # => "Summer Shirt"

This is an example for attr_accesor as it can be used as the getter and as the setter both. For some reason, if we just want to read(get) or just write(set) the attribute then we have the option to use attr_reader or attr_writer as well.