gistfile1.txt

# First rule of pasting code, add comments to explain logic and data structres 
# when it's non-obvious in the code. (Pretty much always) 
class MongoMapperDocument

  # Searches for documents
  # 
  # Structure for `criteria`
  # [
  #   {
  #     "field" => "comments_count"
  #     "operator" => "gte" #or nil
  #     "value" => "4"
  #   },
  # ]
  def self.search(criteria, options={})
    valid_operators = %w(gt lt gte lte ne in nin mod all exists asc desc) #valid for plucky in ruby 1.9, see plucky source
    #protect against invalid operators being called.
    criteria.each do |h|
      unless h["operator"].nil? || valid_operators.include?(h["operator"])
        h["operator"] = nil
      end
    end
    
    new_query = where(options) #allow limits and stuff to be set using `options`
    
    criteria.each do |h|
      #expanded code to make it easier to follow
      field = h["field"].to_sym
      operator = h["operator"].nil? nil : h["operator"].to_sym
      value = h["value"]
      field = field.send(operator) if operator
      #building query, not executed yet.
      new_query = new_query.where(field => value)
    end
    
    return new_query # we return the query, the database has not been hit at this point.
    # The object returns acts like an array. It will load data from the database when it's needed to populate the array.
  end
end

Beware of bugs in the code. I have neither proofed or tested it. ;)