How can I make an aggregated property support ActiveRecord::Dirty semantics?

I have an aggregated attribute which I want to be able ask about its _changed? ness, etc.

composed_of :range,
            :class_name => 'Range',
            :mapping => [ %w(range_begin begin), %w(range_end end)],
            :allow_nil => true

If开发者_JAVA百科 I use the aggregation:

foo.range = 1..10

This is what I get:

foo.range                # => 1..10
foo.range_changed?       # NoMethodError
foo.range_was            # ditto
foo.changed              # ['range_begin', 'range_end']

So basically, I'm not getting ActiveRecord::Dirty semanitcs on aggregated attributes. Is there any way to do that? I'm not having a lot of luck with alias_attribute_with_dirty, etc.

You don't get ActiveRecord::Dirty semantics because aggregated attributes are not association proxies, being mere wrappers for your actual attributes - that's why you have no access to ActiveRecords goodness through them.

Note, that foo.range_begin_changed? should work, so you may try to see if you can use foo.class#method_missing (e.g. defined in a module to be included) to automatically map *_was, *_changed? etc methods to those called on actual attributes of foo.class.