Evil cache bug with composed_of #2084

bradphelan opened this Issue Jul 15, 2011 · 5 comments


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4 participants


The method

235         def writer_method(name, class_name, mapping, allow_nil, converter)
236           define_method("#{name}=") do |part|
237             if part.nil? && allow_nil
238               mapping.each { |pair| self[pair.first] = nil }
239               @aggregation_cache[name] = nil
240             else
241               unless part.is_a?(class_name.constantize) || converter.nil?
242                 part = converter.respond_to?(:call) ?
243                   converter.call(part) :
244                   class_name.constantize.send(converter, part)
245               end
247               mapping.each { |pair| self[pair.first] = part.send(pair.last) }
248               @aggregation_cache[name] = part.freeze
249             end
250           end
251         end

is broken at line 247 due to caching. The problem is that rails does type conversions on activerecord fields. So for example if I have an AR class Foo with a field bar declared as an integer in the db then

foo = new Foo
foo.bar = "10.0"
puts foo.bar.class

=> Integer

However composed_of assumes that the there is no conversion during setting the object. Thus the aggregate objects will be returned with a string field rather than an integer field because the converted object was not read back and put in the cache.
The solution is to add an extra line in the above method that reads back the attribute after writing and caches the converted value and not the original value.

Something like

        def writer_method(name, class_name, mapping, allow_nil, converter)
          define_method("#{name}=") do |part|
            if part.nil? && allow_nil
              mapping.each { |pair| self[pair.first] = nil }
              @aggregation_cache[name] = nil
              unless part.is_a?(class_name.constantize) || converter.nil?
                part = converter.respond_to?(:call) ?
                  converter.call(part) :
                  class_name.constantize.send(converter, part)

              mapping.each { |pair| 
                  self[pair.first] = part.send(pair.last)
                  # Cache the converted attribute in the aggregate part
                  part.send("#{pair.last}=", self[pair.first]
              @aggregation_cache[name] = part.freeze

@bradphelan Is this still an issue, or can it be closed?


Has the suggested fix been made in the code. I don't use composed of anymore. I doubt it has been fixed by some other vector if the change I suggested has not been made.


Since @bradphelan isn't sure if this is still a problem, I'm closing. If anyone wants to produce a test case and/or a patch, I will gladly re-open.

@rafaelfranca rafaelfranca reopened this Apr 29, 2012

Reopening since we got a patch. So it is still an issue


If #6743 gets merged, this bug will go away.

@steveklabnik steveklabnik added a commit that closed this issue Jun 18, 2012
@steveklabnik steveklabnik Removing composed_of from ActiveRecord.
This feature adds a lot of complication to ActiveRecord for dubious
value. Let's talk about what it does currently:

class Customer < ActiveRecord::Base
  composed_of :balance, :class_name => "Money", :mapping => %w(balance amount)

Instead, you can do something like this:

    def balance
      @balance ||= Money.new(value, currency)

    def balance=(balance)
      self[:value] = balance.value
      self[:currency] = balance.currency
      @balance = balance

Since that's fairly easy code to write, and doesn't need anything
extra from the framework, if you use composed_of today, you'll
have to add accessors/mutators like that.

Closes #1436
Closes #2084
Closes #3807
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