Why do ActiveRecord callbacks require instance variables or instance methods to be prefixed with self keyword?

Question

ActiveRecord has a few different callback methods used to simplify model logic. For example after_find and before_create methods.

Consider

Answer 1

Nasmorn is correct.

ActiveRecord::Base placed all the column names inside @attributes instance variable (Hash) and create accessors instance methods for those column names.

For example:

card_status is a column in external_printing_cards table, it will have accessor methods with the name card_status and card_status=

Since ruby local variable definition is dynamic, the line

def after_find
  ....  
  card_status = false if self.is_used_up?
  ....
end

will mean we are defining and assigning to a local variable card_status rather than the instance method card_status=

The article that Peer Allan posted provides more explanation on this.

Answer 2

Technically you only need to use the self in front of the assignment methods. This is necessary to differentiate between a instance method with trailing = and an assignment to a local variable.