Rails - Oct 2006 - What collection type does the has_many macro create?

Can someone explain why you can''t use the return value of an
ActiveRecord::Base collection in a case() statement properly?  Here''s
an example:
>> item = User.find_by_username(''me'').books
[#<Book:0xb771b4b0 ... snip
>> case item; when Array then ''this is an array''; else
"not an array, but a(n) #{item.class}"; end
=> "not an array, but a(n) Array"
>> item === Array
=> true

Can someone explain what''s going on here?  I''m baffled.  The
workaround
I''ve come up with is to insert

  item = item.to_a if item === Array

before the case statement, but that''s sooo hacky.


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On Oct 9, 2006, at 9:43 AM, eden li wrote:
> Can someone explain what''s going on here?  I''m baffled. 
The
> workaround
> I''ve come up with is to insert
>
>   item = item.to_a if item === Array
>
> before the case statement, but that''s sooo hacky.
Indeed, has_many and friends do not return an Array, they return a  
subclass of

   ActiveRecord::Associations::AssociationCollection

defined in

   active_record/associations/association_collection.rb

-- fxn




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What sort of magic is going on to have it return Array as its class
then?  I''m still baffled about the following console output:
>> item.class
=> Array
>> item === Array
=> true

Xavier Noria wrote:
> Indeed, has_many and friends do not return an Array, they return a
> subclass of
>    ActiveRecord::Associations::AssociationCollection
> defined in
>    active_record/associations/association_collection.rb

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On Oct 9, 2006, at 10:34 AM, eden li wrote:
> What sort of magic is going on to have it return Array as its class
> then?  I''m still baffled about the following console output:
>
>>> item.class
> => Array
>>> item === Array
> => true
I got something, ActiveRecord::Associations::AssociationProxy  
redefines === and defines

   def method_missing(method, *args, &block)
     load_target
     @target.send(method, *args, &block)
   end

I traced method_missing is called whenever object.assoc.class is  
called and delegates the call to @target, which is a true Array. That  
explains partially what we see, but I fail to understand why is  
method_missing called at all with a method inherited from Object.

-- fxn




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Xavier Noria wrote:
> I got something, ActiveRecord::Associations::AssociationProxy
> redefines === and defines
>
> ..snip..
Ah, I didn''t think to look one class up.  That explains it.
> ... I fail to understand why is  method_missing called at all
> with a method inherited from Object.
I''m guessing it''s this line (#7 of association_proxy.rb in
rails
1.1.6):

  instance_methods.each { |m| undef_method m unless m =~
/(^__|^nil\?|^proxy_respond_to\?|^proxy_extend|^send)/ }


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On Oct 9, 2006, at 2:32 PM, Xavier Noria wrote:
> On Oct 9, 2006, at 10:34 AM, eden li wrote:
>
>> What sort of magic is going on to have it return Array as its class
>> then?  I''m still baffled about the following console output:
>>
>>>> item.class
>> => Array
>>>> item === Array
>> => true
>
> I got something, ActiveRecord::Associations::AssociationProxy
> redefines === and defines
>
>    def method_missing(method, *args, &block)
>      load_target
>      @target.send(method, *args, &block)
>    end
>
> I traced method_missing is called whenever object.assoc.class is
> called and delegates the call to @target, which is a true Array. That
> explains partially what we see, but I fail to understand why is
> method_missing called at all with a method inherited from Object.
Oh yes, there''s this at the top of that class

   instance_methods.each { |m| undef_method m unless m =~ /(^__|^nil 
\?|^proxy_respond_to\?|^proxy_extend|^send)/ }

which effectively removes Object#class and thus method_missing is  
triggered.

We are getting closer, but not yet explaining that === fails to match  
Array in the case statement.

-- fxn


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It looks like Ruby doesn''t even use the === operator in the case()
statement:

irb(main):005:0> class C; def ===(k); puts "called=== with
#{k.inspect}";true; end; end
=> nil
irb(main):006:0> case C.new; when String; ''string''; else;
''not''; end
=> "not"
irb(main):007:0> C.new===String
called=== with String
=> true

Maybe this question is ready to be ported over to ruby-talk.

Xavier Noria wrote:
> We are getting closer, but not yet explaining that === fails to match
> Array in the case statement.

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eden li <eden.li@...> writes:
> 
> Xavier Noria wrote:
> > I got something, ActiveRecord::Associations::AssociationProxy
> > redefines === and defines
> >
> > ..snip..
> 
It''s also useful to understand that a === b often isn''t the
same as b === a

irb(main):001:0> 1 === Fixnum
=> false
irb(main):002:0> Fixnum === 1
=> true

case 1; when Fixnum; end # Will actually compare Fixnum === 1


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On Oct 9, 2006, at 3:09 PM, eden li wrote:
> It looks like Ruby doesn''t even use the === operator in the case()
> statement:
>
> irb(main):005:0> class C; def ===(k); puts "called=== with
> #{k.inspect}";true; end; end
> => nil
> irb(main):006:0> case C.new; when String; ''string'';
else; ''not''; end
> => "not"
> irb(main):007:0> C.new===String
> called=== with String
> => true
>
> Maybe this question is ready to be ported over to ruby-talk.
Great!


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Ah, that''s it.  So AssociationProxy won''t ever be able to
intercept the
=== call in the case/when, thus never allowing it to match the "when
Array" statement.  That clears it up...

Gareth Adams wrote:
> case 1; when Fixnum; end # Will actually compare Fixnum === 1

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