def getall(self):
        try:
            spec = {'data': {'$exists': 1}}
            fields = {'_id': 0}
            sort = [('tid', 1)]
            cur = self.db.docs.find(spec, fields, sort=sort)
        except Exception as e:
            raise DatabaseException(e)
        return [Document(**row) for row in cur]
def __init__(self, p1, p2):
        self.p1 = p1
        self.p2 = p2
        # 直線的第一點, 設為線尾
        self.Tail = self.p1
        # 直線組成的第二點, 設為線頭
        self.Head = self.p2
        # 直線的長度屬性
        self.length = math.sqrt(math.pow(self.p2.x-self.p1.x, 2)+math.pow(self.p2.y-self.p1.y,2))