Rails - Nov 2009 - Problem with has_many :through, :uniq => true with polymorph

Didn''t have quite enough space to describe it there...basically
i''m
having a problem with the :uniq option in my tags.

I''m using acts_as_taggable_on_steroid which adds these associations to
my Resource class:

Resource
  has_many :taggings, :as => :taggable, :dependent => :destroy, :include
=> :tag
  has_many :tags, :through => :taggings, :uniq => true

This uses the join model Tagging:

Tagging
  belongs_to :tag
  belongs_to :taggable, :polymorphic => true

And of course the Tag model:

Tag
  has_many :taggings, :dependent => :destroy
  has_many_polymorphs :taggables,
    :from => [:resources, :lessons],
    :through => :taggings,
    :dependent => :destroy

The uniq option doesn''t seem to stop me from adding the same tag
multiple times to a resource:
>> resource = Resource.first
=> #<TeachingObject id: 59, name: "Clarinet bite point close-up"
...>
>> tag = Tag.first
=> #<Tag id: 1, name: "recorder">
>> resource.tags
=> [#<Tag id: 1, name: "recorder">, #<Tag id: 610, name:
"chunky
chicken">, #<Tag id: 1, name:
"recorder">]
>> resource.tags << tag
=> [#<Tag id: 1, name: "recorder">, #<Tag id: 610, name:
"chunky
chicken">, #<Tag id: 1, name: "recorder">, #<Tag id:
1, name:
"recorder">]
>> resource.tags << tag
=> [#<Tag id: 1, name: "recorder">, #<Tag id: 610, name:
"chunky
chicken">, #<Tag id: 1, name: "recorder">, #<Tag id:
1, name:
"recorder">, #<Tag id: 1, name: "recorder">]

Now, i have other classes which use has_many :through with :uniq => true
and they seem fine: for example. resources also join to assets, through
a table called ''items'':

Resource
  has_many :items, :dependent => :destroy, :order => :position
  has_many :assets, :through => :items, :order => :position, :uniq =>
true

Item
  belongs_to :asset
  belongs_to :resource

Asset
  has_many :items, :dependent => :destroy, :order => :position
  has_many :resources, :through => :items, :order => :position

Like i say, this behaves as i''d expect:
>> resource = Resource.first
=> #<TeachingObject id: 59, name: "Clarinet bite point close-up"
... >
>> asset = Asset.first
=> #<Asset id: 1, name: "07 Clari Clari (notation, perf AI)" ...
>
>> resource.assets
=> []
>> resource.assets << asset
=> [#<Asset id: 1, name: "07 Clari Clari (notation, perf AI)"
... >]
>> resource.assets << asset
=> [#<Asset id: 1, name: "07 Clari Clari (notation, perf AI)"
... >]

See?  It doesn''t add the duplicate.

I''m wondering if it''s to do with the polymorphic nature of the
tag -
resource relationship - maybe the polymorphism is stopping it from
noticing that it''s not uniq?  or something?

Grateful for any help or ideas...i can''t even think of a way to work
around this since the problem is buried inside active record''s <<
method.
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