What is the right way to override a setter method in Ruby on Rails?

===========================================================================Update: July 19, 2017

Now the Rails documentation is also suggesting to use super like this:

class Model < ActiveRecord::Base  def attribute_name=(value)    # custom actions    ###    super(value)  endend

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Original Answer

If you want to override the setter methods for columns of a table while accessing through models, this is the way to do it.

class Model < ActiveRecord::Base  attr_accessible :attribute_name  def attribute_name=(value)    # custom actions    ###    write_attribute(:attribute_name, value)    # this is same as self[:attribute_name] = value  endend

See Overriding default accessors in the Rails documentation.

So, your first method is the correct way to override column setters in Models of Ruby on Rails. These accessors are already provided by Rails to access the columns of the table as attributes of the model. This is what we call ActiveRecord ORM mapping.

Also keep in mind that the attr_accessible at the top of the model has nothing to do with accessors. It has a completely different functionlity (see this question)

But in pure Ruby, if you have defined accessors for a class and want to override the setter, you have to make use of instance variable like this:

class Person  attr_accessor :nameendclass NewPerson < Person  def name=(value)    # do something    @name = value  endend

This will be easier to understand once you know what attr_accessor does. The code attr_accessor :name is equivalent to these two methods (getter and setter)

def name # getter  @nameenddef name=(value) #  setter  @name = valueend

Also your second method fails because it will cause an infinite loop as you are calling the same method attribute_name= inside that method.

Use the super keyword:

def attribute_name=(value)  super(value.some_custom_encode)end

Conversely, to override the reader:

def attribute_name  super.some_custom_decodeend

In rails 4

let say you have age attribute in your table

def age=(dob)       now = Time.now.utc.to_date    age = now.year - dob.year - ((now.month > dob.month || (now.month == dob.month && now.day >= dob.day)) ? 0 : 1)    super(age) #must add this otherwise you need to add this thing and place the value which you want to save.   end

Note:For new comers in rails 4 you don't need to specify attr_accessible in model. Instead you have to white-list your attributes at controller level using permit method.