Rails has_many through filtered associations - ruby-on-rails

Question

I am trying to use one join model for two separate but very similar associations. Here is what I have:
Two primary models: Package, Size
Pacakges have many sizes but there's a wrinkle. The sizes need to be allocated as a size for top or bottom. My current associations on Package are:
has_many :package_sizes
has_many :sizes, :through => :package_sizes
has_many :bottoms_sizes, :through => :package_sizes, :scope => {:package_sizes => {:bodylocation => "B"}}, :source => :size
has_many :tops_sizes, :through => :package_sizes, :scope => {:package_sizes => {:bodylocation => "T"}}, :source => :size
PackageSize is a join model with: size_id | package_id | bodylocation:string
I have a failing test to verify it is working:
#p = Package.new
#size1 = Size.first
#p.tops_sizes << #size1
#p.save
#p.reload
#p.tops_sizes.should include(#size1)
This should work properly but for some reason the bodylocation field does not get automatically set.
Any ideas?

Answer 1

There is (IMHO) a better solution to this in the answer to: Scope with join on :has_many :through association.
Essentially it would be something like:
has_many :package_sizes
has_many :sizes, :through => :package_sizes do
def tops
where("package_sizes.bodylocation = 'T'")
end
def bottoms
where("package_sizes.bodylocation = 'B'")
end
end
You would then query for them like:
#p.sizes.tops

Answer 2

Try creating two separate through associations for this.
has_many :bottom_package_sizes, :class_name => 'PackageSize', :conditions => {:bodylocation => 'B'}
has_many :top_package_sizes, :class_name => 'PackageSize', :conditions => {:bodylocation => 'T'}
has_many :bottom_sizes, :through => :bottom_package_sizes
has_many :top_sizes, :through => :top_package_sizes