Rails - Feb 2008 - NoMethodError: undefined method `<=>' for :zip:Symbol

Long time programmer, but I just started learning RoR last week. I am
going through some examples in the book "Ruby on Rails: Up and
Running".

The example I am on had me add a table to the database that looks like
so:
CREATE TABLE people (
  `id` int(11) NOT NULL auto_increment,
  `type` varchar(20) default NULL,
  `name` varchar(20) default NULL,
  `email` varchar(30) default NULL,
  `street_address` varchar(30) default NULL,
  `city` varchar(30) default NULL,
  `state` varchar(20) default NULL,
  `zip` int(5) default NULL,
  `camera` varchar(20) default NULL,
  PRIMARY KEY  (`id`)
)

In addition, I created the following two classes:

class Person < ActiveRecord::Base
  composed_of :address, :class_name => "Address",
              :mapping => [[:street_address, :street_address],
                           [:city, :city],
                           [:state, :state],
                           [:zip, :zip]]
end

class Address
  def initialize(street_address, city, state, zip)
    @street_address = street_address
    @city = city
    @state = state
    @zip = zip
  end

  attr_reader :street_address, :city, :state, :zip
end

Finally, it had me run the following commands in Console:
>> elvis.name=Person.new
elvis.name=Person.new
NameError: undefined local variable or method `elvis'' for #<Object:
0x284f9e8>
	from (irb):1
>> elvis=Person.new
elvis=Person.new
=> #<Person id: nil, type: nil, name: nil, email: nil, street_address:
nil, city: nil, state: nil, zip: nil, camera: nil>
>> elvis.name="Elvis Presley"
elvis.name="Elvis Presley"
=> "Elvis Presley"
>> elvis.email="elvis-u/OeZctXj4z2eFz/2MeuCQ@public.gmane.org"
elvis.email="elvis-u/OeZctXj4z2eFz/2MeuCQ@public.gmane.org"
=>
"elvis-u/OeZctXj4z2eFz/2MeuCQ@public.gmane.org"
>> address=Address.new("3734 Elvis Presley Blvd",
"Memphis", "Tennessee", 38118)
address=Address.new("3734 Elvis Presley Blvd", "Memphis",
"Tennessee",
38118)
=> #<Address:0x3f3ce94 @street_address="3734 Elvis Presley
Blvd",
@zip=38118, @state="Tennessee",
@city="Memphis">
>> elvis.address=address
elvis.address=address
=> #<Address:0x3f3ce94 @street_address="3734 Elvis Presley
Blvd",
@zip=38118, @state="Tennessee",
@city="Memphis">
>> elvis.save
elvis.save

However, when I ran the latter-most command, "elvis.save" I received
the following (abbreviated) error:

NoMethodError: undefined method `<=>'' for :zip:Symbol
	from C:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
active_record/base.rb:2177:in `sort''
	from C:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
active_record/base.rb:2177:in `attribute_names''
	from C:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
active_record/base.rb:2458:in `clone_attributes''
...

Why is the method ''<=>'' being attempted on the zip
field?
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On 25 Feb 2008, at 19:26, mrkylehayes-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
wrote:
>
> In addition, I created the following two classes:
>
> class Person < ActiveRecord::Base
>  composed_of :address, :class_name => "Address",
>              :mapping => [[:street_address, :street_address],
>                           [:city, :city],
>                           [:state, :state],
>                           [:zip, :zip]]
> end
>
>
> However, when I ran the latter-most command, "elvis.save" I
received
> the following (abbreviated) error:
>
> NoMethodError: undefined method `<=>'' for :zip:Symbol
> 	from C:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> active_record/base.rb:2177:in `sort''
> 	from C:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> active_record/base.rb:2177:in `attribute_names''
> 	from C:/ruby/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> active_record/base.rb:2458:in `clone_attributes''
> ...
>
> Why is the method ''<=>'' being attempted on the zip
field?
it''s not calling <=> on the zip field itself but on the mapping
you''ve
supplied, which is expected to contain strings
> :mapping => [%w(street_address street_address),
>                           %w(city city),
>                           %w(state state),
>                           %w(zip zip)]
Should do the trick

Fred

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