dm-tags.rb

require "rubygems"
require "dm-core"

class Tag
  include DataMapper::Resource
  
  property :id,             Serial
  property :name,           String
end

class Entry
  include DataMapper::Resource
  
  has n, :tags, :through => Resource
  
  property :id,             Serial
  property :title,          String, :length => 255, :index => true
  
end


DataMapper::Logger.new(STDOUT,:debug)
DataMapper.setup(:default, "sqlite3://#{Dir.pwd}/bula.db")
DataMapper.auto_migrate!


a = Tag.create( :name => "A" )
b = Tag.create( :name => "B" )
Tag.create( :name => "C" )
Tag.create( :name => "D" )

e = Entry.create(:title => "Hello")
e.tags << a
e.tags << b
e.save

e = Entry.create(:title => "World")
e.tags.create( :name => "H" )
e.tags.create( :name => "I" )
e.tags << a
e.save

puts Entry.all( :tags => a ).size # => 1 (expected 2)
puts Entry.all( :tags => b ).size # => 1

# Workaround...
puts Entry.all.select {|e| e.tags.include? a }.size # => 2
puts Entry.all.select {|e| e.tags.include? b }.size # => 1