Class User

    field :name
    has_and_belongs_to_many :tags
    attr_accessible :sports_tag_list, :food_tag_list, :name

    def sports_tag_list=(tag_list)
        # tag_list is a comma separated list.
        # Parse list to individual tag strings
        # to find_or_create tag objects from it.
        # Collect all in tag_obj_array.
        # So, for "Golf, Tennis", tag_obj_array
        # will contain Tag objects for 'Golf' and 'Tennis'
        # both with type 'sports'.
        tag_obj_array.each do |tag|
            self.tags.push(tag) unless self.tags.include?(tag)
        end
    end

    def food_tag_list=(tag_list)
        # Similar to the method above
        # This will add tags with type "food"
        tag_obj_array.each do |tag|
            self.tags.push(tag) unless self.tags.include?(tag)
        end       
    end
    
    def sports_tag_list
        # return comma delimited list of tags with type = 'sports'
    end

    def food_tag_list
        # return comma delimited list of tags with type = 'food'
    end

end

Class Tag
    attr_accessible :name, :type
    field :name
    field :type
    has_and_belongs_to_many :users
end

attrs = {:sports_tag_list => "Golf", :food_tag_list => "Rice"}
u = User.create({:name => "TestUser"})
u.update_attributes(attrs))

Tag.where(name: 'Golf').first.users.count.should == 1
Tag.where(name: 'Rice').first.users.count.should == 1

# Remove 'Golf'
u.update_attributes(attrs.merge(:sports_tag_list => ""))

Tag.where(name: 'Golf').first.users.count.should == 0
Tag.where(name: 'Rice').first.users.count.should == 1

# Add 'Golf' back
u.update_attributes(attrs)

Tag.where(name: 'Golf').first.users.count.should == 1   # THIS FAILS!! Actual value is 0 instead of 1.
Tag.where(name: 'Rice').first.users.count.should == 1