protected function applyWhitelist() {
		if ($this->dbsType == 'sql') {
			// fetch full schema
			if (!$this->fluid && isset(self::$schema_cache[$key=$this->table.$this->db->uuid()]))
				$schema = self::$schema_cache[$key];
			else {
				$schema = $this->mapper->schema();
				self::$schema_cache[$this->table.$this->db->uuid()] = $schema;
			}
			// apply reduced fields schema
			if ($this->whitelist)
				$schema = array_intersect_key($schema, array_flip($this->whitelist));
			$this->mapper->schema($schema);
			$this->mapper->reset();
		}
	}