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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _read_json_db(self):
 """ read metadata from a json string stored in a DB. :return: the parsed json dict :rtype: dict """

        try:
            metadata_str = self.db_io.read_metadata_from_uri(
                self.layer_uri, 'json')
        except HashNotFoundError:
            return {}
        try:
            metadata = json.loads(metadata_str)
            return metadata
        except ValueError:
            message = tr('the file DB entry for %s does not appear to be '
                         'valid JSON')
            message %= self.layer_uri
            raise MetadataReadError(message)