def delete(self, doc):
        if doc.id is None:
            raise DatabaseException('Document does not have id')
        if doc.sid is None:
            try:
                rs = self.db.docs.remove({'id': doc.id}, safe=True)
                assert rs['n'] == 1
            except Exception as e:
                raise DatabaseException(e)
            return None
        doc.data = None
        return self.update(doc)
def _get_unique_constraints(self, table):
    """Retrieve information about existing unique constraints of the table

    This feature is needed for _recreate_table() to work properly.
    Unfortunately, it's not available in sqlalchemy 0.7.x/0.8.x.

    """

    data = table.metadata.bind.execute(
        """SELECT sql
           FROM sqlite_master
           WHERE
               type='table' AND
               name=:table_name""",
        table_name=table.name
    ).fetchone()[0]

    UNIQUE_PATTERN = "CONSTRAINT (\w+) UNIQUE \(([^\)]+)\)"
    return [
        UniqueConstraint(
            *[getattr(table.columns, c.strip(' "')) for c in cols.split(",")],
            name=name
        )
        for name, cols in re.findall(UNIQUE_PATTERN, data)
    ]