If I have a class in Rails:
class Ticket < ActiveRecord::Base
def update_status
return if status == 'sold'
return unless reserved_until.nil? || reserved_until.past?
self.status = 'open'
end
end
where status and reserved_until are fields in the database for the Ticket model, why do I only have to use self when I am assigning a value?
Because if you do status = 'open' you are creating a new local variable called status. That's not about Rails. That is about how Ruby interpreter evaluate your code.
The accepted answer here explains it pretty well. -> When to use self in Model?
To read further in depth this is an excellent blog that puts it clearly. http://www.railstips.org/blog/archives/2009/05/11/class-and-instance-methods-in-ruby/
Whenever you want to invoke a setter method on self, you have to write self.status = "open". If you just write status = "open", the ruby parser recognizes that as a variable assignment and thinks of status as a local variable from now on. For the parser to realize, that you want to invoke a setter method, and not assign a local variable, you have to write obj.status = "open", so if the object is self, self.status = "open"
