code: function build_where_nodes (query, groups, order_fields, operator) {
  	var where_str = "";
  
  	groups.forEach(function (group, index) {
  		var where_query = group.build();
  
  		if (index > 0) {
  			where_str += " " + operator + " ";
  		}
  
  		where_str   += where_query.str;
  		query.values = query.values.concat(where_query.values);
  
  		if (where_query.sort) {
  			order_fields.push(where_query.sort);
  		}
  	});
  
  	return where_str;
  }
docs: Private methods