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What is attr_accessor in Rails?

What is attr_accessor in Rails?

attr_accessor is used to define an attribute for object of Model which is not mapped with any column in database. This answers question - What is attr_accessor in Rails.
1. attr_accessor Methods

attr_accessor creates two methods i.e. getter method and setter method.
getter method - it is used to retrieve value of the attribute
setter method - it is used to set value to the attribute
When to use attr_accessor in Rails?

Whenever you want to show certain attribute for particular form but you do not want to store it's value in the database then you use attr_accessor for that model as follows,
Suppose we have a Model called user in out database with following fields,

    id
    name
    age
    city
    profession

And we define attr_accessor :type_of_user as follows,

Class User < ActiveRecord::Base
   attr_accessor :type_of_user
end

Now, whenever you create a object of the class User then you can assign a value to it's attr_accessor.

new_user = User.new(:name => 'Albert', :age => 23, :city => 'Ports S.')

This will create new object of class User and assign given attribute values. You can assign value to attr_accessor variable as follows,

new_user.type_of_user = 'middle-aged'

This assigns 'middle-aged' value to the attribute type_of_user attr_accessor.
getter and setter in Action

For attribute type_of_user getter and setter methods are created as follows,

# getter
def type_of_user
  @type_of_user
end

# setter
def type_of_user=(val)
  @type_of_user = val
end

And these are used whenever we assign or retrieve values from the attr_accessor.
2. Lifetime of attr_accessor

attr_accessor is accessible throughout object's lifecycle. When object is saved using any of ActiveRecord method, save, update etc. all attributes of Model other than attr_accessor are saved in the database.
How to Access

Throughout lifecycle of object, you can access the value of attribute accessor as follows,

new_user.type_of_user

and can be used for any operation as you do with normal attribute value.

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