Rails - Jul 2007 - ActiveRecord: why does 'self.name' and 'name' both work?

I''m trying to figure out why both ''self.name'' and
''name'' work in a
model class. For example:

class Category < ActiveRecord::Base
  before_save :set_permalink
  private
  def set_permalink
    # both work
    self.permalink = name
    self.permalink = self.name
    # doesn''t work
    permalink = name
    @permalink = name
    @permalink = @name
    self.permalink = @name
  end
end

I thought that attributes in a class were set via instance methods,
but ''self.permalink = @name'' doesn''t work, but
''name'' (which looks
like a local variable to me) works fine. And self.permalink works, but
@permalink doesn''t.

I''m still new to Ruby and classes so it''s probably something
simple I
don''t understand, so any help would be appreciated.


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Basically name and self.name are interpreted by ruby as methods..

because your model when mapped to its corresponding table has a  
column called ''name'', rails creates the relevant method
instance.name.

Therefore your reference to name and self.name are calling the same  
method.. as name (without the self.) is scoped to the instance method  
(as its inside an instance method itself), and self evaluates to the  
instance, therefore it calls the instance method ''name''..

# both work
     self.permalink = name <-- calls method name, and its value is  
passed to the method ''permalink'' (again, not an variable
really)
     self.permalink = self.name <-- calls same method.. as self.  
evaluates to the instance
     # doesn''t work
     permalink = name <-- ruby is probably getting confused here..  
which is probably why its not working..
     @permalink = name <-- again this is probably being set .. but it  
wont update your model as it is saved.. because @permalink is a var  
self.permalink is the method you need to call to update your model..
     @permalink = @name <--- again they are not instance vars. .. so  
@permalink => nil but you wont see it in your db..
     self.permalink = @name <-- @name doesnt exist .. so will be nil..

I hope that makes sense.. sunday afternoon in the office has left my  
brain a bit fried.. (mainly because im writing actionscript..)

Good luck!

Jason.


On 1 Jul 2007, at 17:10, rob wrote:

I''m trying to figure out why both ''self.name'' and
''name'' work in a
model class. For example:

class Category < ActiveRecord::Base
   before_save :set_permalink
   private
   def set_permalink
     # both work
     self.permalink = name
     self.permalink = self.name
     # doesn''t work
     permalink = name
     @permalink = name
     @permalink = @name
     self.permalink = @name
   end
end

I thought that attributes in a class were set via instance methods,
but ''self.permalink = @name'' doesn''t work, but
''name'' (which looks
like a local variable to me) works fine. And self.permalink works, but
@permalink doesn''t.

I''m still new to Ruby and classes so it''s probably something
simple I
don''t understand, so any help would be appreciated.




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