Alias_method in a plugin

Rails
1

Hi all,

I’m trying to override some method of a class. I’ve created an
acts_as_money method. The first parameter is the method name that
should be overridden. For example:

I have a model with an attribute “amount”. I want to be able to do
this:
acts_as_money :amount

Then the amount method should be aliased to an already defined method
in the plugin.
I’ve got this code now:
http://pastie.caboo.se/63676

But then I get this error: NameError: undefined method amount' for class Declaration’

And the Declaration model HAS a method amount. Does anyone now how I
can solve this problem?

2

double check the error and make sure its talking about an instance
method and not a Class method which should not exist

3

This is the precise error:

dec = Declaration.new
NameError: undefined method amount' for class Declaration’
from ./script/…/config/…/config/…/vendor/plugins/
acts_as_money/lib/acts_as_money.rb:12:in instance_method' from ./script/../config/../config/../vendor/plugins/ acts_as_money/lib/acts_as_money.rb:12:in acts_as_money’
from ./script/…/config/…/config/…/app/models/declaration.rb:
19
from /usr/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/
active_support/dependencies.rb:203:in
load_without_new_constant_marking' from /usr/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/ active_support/dependencies.rb:203:in load_file’
from /usr/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/
active_support/dependencies.rb:342:in new_constants_in' from /usr/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/ active_support/dependencies.rb:202:in load_file’
from /usr/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/
active_support/dependencies.rb:94:in require_or_load' from /usr/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/ active_support/dependencies.rb:248:in load_missing_constant’
from /usr/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/
active_support/dependencies.rb:452:in const_missing' from /usr/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/ active_support/dependencies.rb:464:in const_missing’
from (irb):1

On May 23, 2:49 am, Keynan P. [email protected]

4

On 5/22/07, LeonB [email protected] wrote:

Actually, there is no amount method in the Declaration class. Rails
uses method_missing to read the attributes.

If you want to do this, just define the method. In order to read the
amount column’s value, use read_attribute.

define_method(:amount) { “$#{read_attribute(:amount)}” }

Let’s say you need to provide the raw column value for some reason.
read_attribute is private so you can’t use it, plus it breaks
encapsulation, plus it’s just ugly :slight_smile: (d.send :read_attribute,
:amount. bleh)

Go ahead and define an accessor method that does read_attribute for you:

    def acts_as_money(name, options = {})
      define_method(:old_amount) { read_attribute :amount }
      define_method(:amount) { "$#{old_amount}" }
    end

hth

Pat

5

maybe this would be simpler

   def acts_as_money(name, options = {})
      define_method(:"#{name}", "def amount @amount end")

      include LeonB::Acts::Money::InstanceMethods
      extend LeonB::Acts::Money::SingletonMethods
    end
6

Thanks Pat! I never guessed that of method_missing.
Makes sense now.

7

Thanks Pat! I never guessed that of method_missing.
Makes sense now.

8

Thanks Pat! I never guessed that of method_missing.
Makes sense now.