Improving tags map/reduce with MongoDB 1.8.x

tags-mapreduce-mongodb-inline.rb

class Tag
  include Mongoid::Document
  
  def self.rebuild
    tags_before = Hash[ * Tag.all.collect { |tag|
      [tag.name, tag]
    }.flatten]

    map = <<-EOS
        function() { 
          if (this.tags != null) { 
            this.tags.forEach(function(t) { 
              emit(t, 1); 
            }); 
          }
        }
    EOS
    
    reduce = <<-EOS
      function(key, values) { 
        var count = 0; 
        values.forEach(function(v) { count += v; }); 
        return count; 
      }
    EOS

    tags_mapreduce = nil
    tags_mapreduce_coll = nil
    if collection.db.connection.server_version >= '1.7.4'
      tags_mapreduce = TaggedModel.collection.map_reduce(map, reduce, { :raw => true, :out => { :inline => 1 } })['results']
    else
      TaggedModel.collection.map_reduce(map, reduce, { out: 'tags_mapreduce' })
      tags_mapreduce_coll = Mongoid.master.collection('tags_mapreduce')
      tags_mapreduce = tags_mapreduce_coll.find()
    end
    
    tags_after = []
    tags_mapreduce.each do |tag_mapreduce|
      name = tag_mapreduce['_id']
      next if name.nil?
      name = name.strip
      next if name.blank?
      tag = tags_before[name]
      tag_mapreduce_count = tag_mapreduce['value'].to_i
      if ! tag
        Tag.create!(name: name, count: tag_mapreduce_count)
      else        
        if (tag_mapreduce_count != tag.count)
          tag.update_attribute(:count, tag_mapreduce_count)
        end
      end
      tags_after << tag
    end
    
    (tags_before.values - tags_after).each do |tag|
      tag.delete
    end
    
    tags_mapreduce_coll.drop if tags_mapreduce_coll
  end
end