dm-hack.rb

module DataMapper
  module Model
    module Relationship
      alias_method :orig_has, :has
      
      # Overrides has method if:
      # 1. It's ManyToMany
      # 2. Share the same storage
      #
      # And then modify the table to save the relationship ids in a string instead of
      # a A_B table.
      #
      # This is to avoid "ambiguous column name"-errors in DataMapper 0.10.2
      #
      def has(cardinality, name, *args)
        options = extract_options(args)
        model = ( options[:model] || name ).to_s.singularize.to_const_string.constantize
        if cardinality == n && options.key?( :through ) && options[:through] == Resource && self.storage_name(repository_name) == model.storage_name(repository_name)
          # 1. Create a property
          property :"#{name}_ids", String, :length => 65000, :default => ""
        
          # 2. Create a reader 
          class_eval <<-RUBY, __FILE__, __LINE__ + 1
            def #{name}(query=nil)
              @#{name} ||= #{model}.all( (query||{}).merge( :id => #{name}_ids.split(",") ) )
            end
          RUBY
        
          # 3. Create a hook
          class_eval <<-RUBY, __FILE__, __LINE__ + 1
            before :save do
              if @#{name}
                self[:"#{name}_ids"] = @#{name}.map {|r| r.id }.join(",") 
                @#{name} = nil
              end
            end
          RUBY
        else
          orig_has( cardinality , name , *args )
        end
      end
      
    end
  end
end