Rails - Jun 2007 - problem with AR and 'virtual' multiparameter attributes.

Hello,

I have a model which I would like to have a ''virtual'' date
column.
This column wouldn''t exist in the database, but would exist for
validation, etc. The data would be provided in the form of a
date_select in the view. This produces a multiparameter attribute. My
problem is that the
''execute_callstack_for_multiparameter_attributes''
method in base.rb of ActiveRecord looks at the columns array to
determine the ''class'' (klass) to use when doing the
multiparameter
conversion.  Since this column doesn''t really exist nothing is found
and an exception is thrown when trying to evaluate nil.klass.

I''m willing to provide a patch, but I am not what would be the best
way to provide the type information. Any suggestions?

Thanks,

-James


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James wrote:
> Hello,
> 
> I have a model which I would like to have a ''virtual''
date column.
> This column wouldn''t exist in the database, but would exist for
> validation, etc. The data would be provided in the form of a
> date_select in the view. This produces a multiparameter attribute. My
> problem is that the
''execute_callstack_for_multiparameter_attributes''
> method in base.rb of ActiveRecord looks at the columns array to
> determine the ''class'' (klass) to use when doing the
multiparameter
> conversion.  Since this column doesn''t really exist nothing is
found
> and an exception is thrown when trying to evaluate nil.klass.
> 
> I''m willing to provide a patch, but I am not what would be the
best
> way to provide the type information. Any suggestions?
> 
> Thanks,
> 
> -James
Hi, I have this same issue, it looks like the 
execute_callstack_for_multiparameter_attributes assumes that all 
muti-parameter attributes are persistent.

the code in there is way over my head also, does anyone have suggestions 
of how to get this to work? or an elegant work around? (for now im going 
to roll my own time_select helper I guess)

To reproduce this issue, add attr_accessor :foo to any active record and 
then try to use a helper that is multi parameter (time,date etc) like 
time_select on it. On submit you will get:

NoMethodError (You have a nil object when you didn''t expect it!
The error occurred while evaluating nil.klass):
/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/base.rb:2082:in 
`execute_callstack_for_multiparameter_attributes''
/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/base.rb:2081:in 
`execute_callstack_for_multiparameter_attributes''
/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/base.rb:2074:in 
`assign_multiparameter_attributes''
/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/base.rb:1675:in 
`attributes=''
/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/base.rb:1505:in 
`initialize_without_callbacks''
/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/callbacks.rb:225:in
`initialize''
/app/controllers/tasks_controller.rb:534:in `create''
/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_controller/base.rb:1095:in 
`perform_action_without_filters''
/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_controller/filters.rb:632:in
`call_filter''
/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_controller/filters.rb:638:in
`call_filter''
/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_controller/filters.rb:438:in
`call''
/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_controller/filters.rb:637:in
`call_filter''
/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_controller/filters.rb:634:in
`call_filter''
/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_controller/filters.rb:638:in
`call_filter''
/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_controller/filters.rb:438:in
`call''

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

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On Dec 11, 1:39 pm, Joel Nylund
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
> > I''m willing to provide a patch, but I am not what would be
the best
> > way to provide the type information. Any suggestions?
Did you end up writing anything?  Running into this problem myself and
am handling it with the controller re-writing the params[:hash] as an
"instant" fix.

I''ll look into it as well if you haven''t.

Mikel
http://lindsaar.net/


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