From: Rick DeNatale <rick.denatale@...>
Date: 2010-01-09T05:33:43+09:00
Subject: Re: Something changed an instance variable ... and now I'm confused

On Fri, Jan 8, 2010 at 12:05 PM, Ralph Shnelvar <ralphs@dos32.com> wrote:
> Newbie here.
>
> Consider this irb session ...
>
>
> F:\InstantRails-2.0-win\rails_apps>irb
> irb(main):001:0> class X
> irb(main):002:1>   attr_accessor :x, :y
> irb(main):003:1> end
> => nil
> irb(main):004:0>
> irb(main):005:0* x1 = X.new
> => #<X:0x29211a0>
> irb(main):006:0>
> irb(main):007:0* x1.x = 5;
> irb(main):008:0* x1.y = 6;
> irb(main):009:0*
> irb(main):010:0*
> irb(main):011:0*
> irb(main):012:0* class X
> irb(main):013:1>   def x=(arg)
> irb(main):014:2>     puts "arg=" + arg.to_s
> irb(main):015:2>     @x = arg
> irb(main):016:2>     puts "whoopy"
> irb(main):017:2>     @x
> irb(main):018:2>   end
> irb(main):019:1>
> irb(main):020:1*   def make_x
> irb(main):021:2>     self.x = "xyzzy"
> irb(main):022:2>   end
> irb(main):023:1> end
> => nil
> irb(main):024:0>
> irb(main):025:0*
> irb(main):026:0* x1.x = "hello"
> arg=hello
> whoopy
> => "hello"
> irb(main):027:0> x1
> => #<X:0x29211a0 @y=6, @x="hello">
> irb(main):028:0> x1.make_x
> arg=xyzzy
> whoopy
> => "xyzzy"
> irb(main):029:0> x1
> => #<X:0x29211a0 @y=6, @x="xyzzy">
> irb(main):030:0>
>
>
>
> The background ...
>
> I am debugging an RoR application and noticed that the @activation_code instance variable was being modified _somewhere_.  I couldn't tell where.
>
> So I added a method to the User class
>
>  def activation_code=(arg)
>    puts at_file_line_msg(__FILE__, __LINE__)
>          puts "arg=" + arg
>    @activation_code=arg
>    debugger
>    @activation_code
>  end
>
>
> When I look at the value of @activation_code in the debugger (at the debuuger breakpoint), it has the right value ...
>
> but when I look at self in the debugger, the activation_code field is nil.
>
> I do not understand why things seem to work in the snippet of code I provided, above, in irb ... but do not work in the far more complex RoR environment.

Is activation_code an attribute of an ActiveRecord model?

If so then the value isn't stored in an instance variable, the
accessors are actually handled via method_missing. By defining
activation_code= you are preventing activerecord from doing it's
thing.

You need something like:

def activation_code=(arg)
    puts at_file_line_msg(__FILE__, __LINE__)
          puts "arg=" + arg
    self['activation_code'] =arg
    debugger
    arg    # strictly speaking you don't really need this since ruby
assignments via an x= method ignore the return value
end


-- 
Rick DeNatale

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