Extract query pattern from operations.

def command(self):
        """Extract query pattern from operations."""
        if not self._command_calculated:

            self._command_calculated = True
            if self.operation == 'command':
                try:
                    command_idx = self.split_tokens.index('command:')
                    command = self.split_tokens[command_idx + 1]
                    if command == '{':
                        # workaround for <= 2.2 log files,
                        # where command was not listed separately
                        command = self.split_tokens[command_idx + 2][:-1]
                    self._command = command.lower()
                except ValueError:
                    pass

        return self._command