def get_next_id(self):
        try:
            query = {'_id': 'last_id'}
            update = {'$inc': {'id': 1}}
            fn = self.db.internal.find_and_modify
            row = fn(query, update, upsert=True, new=True)
        except Exception as e:
            raise DatabaseException(e)
        return row['id']
def setPPSS(self, p1, p3, lenp1, lenp3):
        temp = []
        self.p1 = p1
        self.p3 = p3
        self.lenp1 = lenp1
        self.lenp3 = lenp3

        #bp3 is the angle beside p3 point, cp3 is the angle for line23, p2 is the output
        line31 = Line(p3, p1)
        self.lenp2 = line31.getR()
        #self.lenp2 = self.p3.distance(self.p1)
        #這裡是求角3
        ap3 = math.acos(((self.lenp1 * self.lenp1 + self.lenp2 * self.lenp2) - self.lenp3 * self.lenp3) / (2 * self.lenp1 * self.lenp2))
        #ap3 = math.acos(((self.lenp1 * self.lenp1 + self.lenp3 * self.lenp3) - self.lenp2 * self.lenp2) / (2 * self.lenp1 * self.lenp3))
        bp3 = line31.getT()
        cp3 = bp3 - ap3
        temp.append(p3.x + self.lenp1*math.cos(cp3))#p2.x
        temp.append(p3.y + self.lenp1*math.sin(cp3))#p2.y
        return temp