Rails - Jul 2006 - Tableless ActiveRecord attribute and my aching head

I beat my head against a wall for almost 2 hours with this issue.

My first problem was easily solved.  I wanted a class that could use 
ActiveRecord''s validation capabilities but without using a table behind
it (I would be persisting setup information in the session, but the 
initial setup parameters come from a user input form)

No problem...found this link which got me up and running

http://rails.techno-weenie.net/tip/2005/11/19/validate_your_forms_with_a_table_less_model

This was the class definition I ended up with:

-------------------------------------
class Setup < ActiveRecord::Base
 def self.columns() @columns ||= []; end
 def self.column(name, sql_type = nil, default = nil, null = true)
     columns << ActiveRecord::ConnectionAdapters::Column.new(name.to_s, 
default, sql_type.to_s, null)
 end

 ...
 column :turn, :integer
 ...

def change_turn
   if turn==0
     turn = 1
   else
     turn = 0
   end
end

end
--------------------------------


ok....
now the head-banger.  Any time I called the ''change_turn''
method inside
my new class, the turn wouldn''t actually be changed.  Oh, I would put 
logger_debug statements inside the change_turn method itself and the 
value WAS being changed, but the changes weren''t visible OUTSIDE the 
class.  Er?

It wasn''t until I changed the ''change_turn'' method to
look like this
that it started working properly:

def change_turn
   if turn==0
     self[:turn] = 1
   else
     self[:turn] =0
   end
end

why!!!???  If I can reference the ''turn'' attribute simply by
calling it
''turn (as in ''if turn==0'') then why cant I set the
value by referencing
it the same way (by name)????
Is this in some way related to my abuse of ActiveRecord?  Or is this 
true of any Ruby class?

My head hurts and I am tired.  I assume that I am missing something 
basic here...

Any insight would be appreciated.


-- 
Posted via http://www.ruby-forum.com/.

Try self[:turn]. I don''t think you''re affecting the state of
your model.
-- 
View this message in context:
http://www.nabble.com/Tableless-ActiveRecord-attribute--and-my-aching-head-tf1982503.html#a5441400
Sent from the RubyOnRails Users forum at Nabble.com.

turn == 0 looks first for a local variable called turn, doesn''t find
it, so runs the turn method on the object.

turn = 0 (or turn = 1) defines a LOCAL variable called turn, that is
scoped to this method call. Because you want to run the turn method on
the object itself, use self.turn instead.

It is a bit confusing, but it does make sense. If you wrote a = 1 in
that method, you would not expect ruby to run the a method on the
object, you would expect it to create a local variable called a, which
is exactly what it does.

self.turn = 0 will work.

-Jonathan.

On 7/22/06, J Amiel <jeff.amiel@gmail.com> wrote:
> I beat my head against a wall for almost 2 hours with this issue.
>
> My first problem was easily solved.  I wanted a class that could use
> ActiveRecord''s validation capabilities but without using a table
behind
> it (I would be persisting setup information in the session, but the
> initial setup parameters come from a user input form)
>
> No problem...found this link which got me up and running
>
>
http://rails.techno-weenie.net/tip/2005/11/19/validate_your_forms_with_a_table_less_model
>
> This was the class definition I ended up with:
>
> -------------------------------------
> class Setup < ActiveRecord::Base
>  def self.columns() @columns ||= []; end
>  def self.column(name, sql_type = nil, default = nil, null = true)
>      columns <<
ActiveRecord::ConnectionAdapters::Column.new(name.to_s,
> default, sql_type.to_s, null)
>  end
>
>  ...
>  column :turn, :integer
>  ...
>
> def change_turn
>    if turn==0
>      turn = 1
>    else
>      turn = 0
>    end
> end
>
> end
> --------------------------------
>
>
> ok....
> now the head-banger.  Any time I called the ''change_turn''
method inside
> my new class, the turn wouldn''t actually be changed.  Oh, I would
put
> logger_debug statements inside the change_turn method itself and the
> value WAS being changed, but the changes weren''t visible OUTSIDE
the
> class.  Er?
>
> It wasn''t until I changed the ''change_turn''
method to look like this
> that it started working properly:
>
> def change_turn
>    if turn==0
>      self[:turn] = 1
>    else
>      self[:turn] =0
>    end
> end
>
> why!!!???  If I can reference the ''turn'' attribute simply
by calling it
> ''turn (as in ''if turn==0'') then why cant I set
the value by referencing
> it the same way (by name)????
> Is this in some way related to my abuse of ActiveRecord?  Or is this
> true of any Ruby class?
>
> My head hurts and I am tired.  I assume that I am missing something
> basic here...
>
> Any insight would be appreciated.
>
>
> --
> Posted via http://www.ruby-forum.com/.
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> Rails mailing list
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>