def find_by_index(self, cls, index_name, value):
        """Find all rows matching index query - as per the gludb spec."""
        cur = self._conn().cursor()

        # psycopg2 supports using Python formatters for queries
        # we also request our JSON as a string for the from_data calls
        query = 'select id, value::text from {0} where {1} = %s;'.format(
            cls.get_table_name(),
            index_name
        )

        found = []
        with self._conn() as conn:
            with conn.cursor() as cur:
                cur.execute(query, (value,))
                for row in cur:
                    id, data = str(row[0]).strip(), row[1]
                    obj = cls.from_data(data)
                    assert id == obj.id
                    found.append(obj)

        return found
Find all rows matching index query - as per the gludb spec.