Return comments for :param:`uri` with :param:`mode`.

def fetch(self, uri, mode=5, after=0, parent='any',
              order_by='id', asc=1, limit=None):
        """
        Return comments for :param:`uri` with :param:`mode`.
        """
        sql = ['SELECT comments.* FROM comments INNER JOIN threads ON',
               '    threads.uri=? AND comments.tid=threads.id AND (? | comments.mode) = ?',
               '    AND comments.created>?']

        sql_args = [uri, mode, mode, after]

        if parent != 'any':
            if parent is None:
                sql.append('AND comments.parent IS NULL')
            else:
                sql.append('AND comments.parent=?')
                sql_args.append(parent)

        # custom sanitization
        if order_by not in ['id', 'created', 'modified', 'likes', 'dislikes']:
            order_by = 'id'
        sql.append('ORDER BY ')
        sql.append(order_by)
        if not asc:
            sql.append(' DESC')

        if limit:
            sql.append('LIMIT ?')
            sql_args.append(limit)

        rv = self.db.execute(sql, sql_args).fetchall()
        for item in rv:
            yield dict(zip(Comments.fields, item))