[Rails-core] Some aggregation issues.

[Peter Haight]

I've had a couple of instances where I've wanted to work with an attribute in
an ActiveRecord through another class. For example I'm storing time zones in
my database as strings, but I want to always deal with them through a
TimeZone object. Same goes for time intervals.

I've been using aggregations to do with with some success, but if someone can
suggest a more appropriate way, please let me know.

If aggregations are the right way to go, I've got some issues.

First, if you've got aggregations all setup to work to convert from the
database, they still don't seem to get handled when converting from a web
form (via update_attributes). I then stumbled on to multiparameter
attributes, which seems to know about aggregations. That was working for a
tag where I generate the name myself "employee[time_zone(1)]", but causes an
error if you try to use text_field('employee', 'time_zone(1)'). 

I think that the FormHelper should handle multiparameter attribute syntax, if
people agree, I'll do a patch for it.

Then I thought about it, and I think you shouldn't have to use the
multiparameter syntax in the case where you have an aggregation with just one
parameter. It should just do the cast automatically. So, I came up with the
patch at the end of this mail.

It seems to work ok for me, but I thought I'd see what other people have to
say before doing any more work on it.


--- activerecord-1.13.2/lib/active_record/base.rb.orig  Fri Jan 13 15:58:45 2006
+++ activerecord-1.13.2/lib/active_record/base.rb   Wed Jan 25 18:50:27 2006
@@ -1334,7 +1334,17 @@
 
 multi_parameter_attributes = []
 remove_attributes_protected_from_mass_assignment(attributes).each do 
|k, v|
-  k.include?("(") ? multi_parameter_attributes << [ k, v ] : send(k + 
"=", v)
+  if k.include?("(")
+multi_parameter_attributes << [ k, v ]
+next
+  end
+ reflection = self.class.reflect_on_aggregation(k.to_sym)
+  if reflection
+   klass = reflection.klass
+   send(k + "=", Time == klass ? klass.local(v) : klass.new(v))
+next
+ end
+ send(k + "=", v)
 end
 assign_multiparameter_attributes(multi_parameter_attributes)
   end


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Re: [Rails-core] How should we do away with the rubysess white page of death?

[Peter Haight]

> > At a slight tangent, isolating application sessions won't fully solve
> > this problem; you can change the name of a Model object and see this
> > 'white screen of death' within the same application. Something needs
> > to be wrapped around the session loading to let Rails gracefully
> > handle loading a malignant session and at least give the user *some*
> > feedback (logs, 500 status, anything really).
> >
> 
> The root of the issue here is that CGI::Session doesn't raise an  
> exception when this sort of behavior occurs.  It's awful, I know, but  
> it's the sad truth: there's no way to know in advance if
> 
>   request  = ActionController::CgiRequest.new(cgi, session_options)
> 
> will totally fail or not, and there's no exception raised.  It's even  
> in the docs that "things will break nastily" [1] in just this sort of  
> situation.  If I am wrong here (and I'd love to be) then please let  
> me know.

Actually, it does raise an exception (at least in the case where it can't
open the session file due to permissions issues). But the error handling path
assumes the presense of a working session object so the exception never gets
logged.  I filed that bug here: http://dev.rubyonrails.org/ticket/3474.


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