gistfile1.rb

#!/usr/bin/env ruby  
  
require 'rubygems'  
  
gem 'dm-core', '=0.9.10'  
require 'dm-core'  
 
# uncomment for logging output
 
#DataMapper::Logger.new(STDOUT, :debug)
  
DataMapper.setup(:default, 'sqlite3::memory:')  

class Branch
  
  include DataMapper::Resource
  
  property :id,   Serial
  property :name, String
  
  has n, :branch_items
  has n, :items, :through => :branch_items
  
  has n, :featured_branch_items, 
    :class_name => 'BranchItem', 
    :child_key => [ :branch_id ], 
    :featured => true
  
  # i would expect this to be scoped to
  # only featured branch_items
  has n, :featured_items, 
    :through => :featured_branch_items, 
    :class_name => 'Item', 
    :child_key => [ :branch_id ], 
    :remote_name => :item
    
    # i also tried: (uncomment to try for yourself)
    
    # 'branch_items.featured' => true
    # => Unknown property 'branch_items' (ArgumentError)
        
    # :featured => true
    # => Unknown property 'featured' (ArgumentError)
    
end

class Item
  
  include DataMapper::Resource
  
  property :id,   Serial
  property :name, String

end

class BranchItem
  
  include DataMapper::Resource
  
  property :id,        Serial
  property :branch_id, Integer, :nullable => false
  property :item_id,   Integer, :nullable => false
  property :featured,  Boolean, :default => false
  
  belongs_to :branch
  belongs_to :item
  
end


DataMapper.auto_migrate!


b = Branch.create(:name => 'foo_branch')
i01 = Item.create(:name => 'foo_item')
i02 = Item.create(:name => 'bar_item')

BranchItem.create(:branch => b, :item => i01, :featured => true)
BranchItem.create(:branch => b, :item => i02)

b = Branch.get(1)
puts "b.items.size: #{b.items.size}"                                 # correctly prints "2"
puts "b.featured_items.size: #{b.featured_items.size}"               # incorrectly prints "2"
puts "b.featured_branch_items.size: #{b.featured_branch_items.size}" # correctly prints "1"