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我有兩個型號，組合鍵：複合鍵
class ContestUser(models.Model):
user_id = models.IntegerField(primary_key = True)
contest_id = models.IntegerField(primary_key = True)
username = models.CharField(max_length = 1536, blank = True)
.
.
.
class ContestRegistration(models.Model):
user_id = models.IntegerField(primary_key = True)
contest_id = models.IntegerField(primary_key = True)
status = models.IntegerField(choices = EJUDGE_CONTEST_STATUSES)
.
.
.
首先的問題是如何能與他們和查詢一樣加入進來。
從ContestRegistration中選擇*加入ContestUser在r.user_id = u.user_id和r.contest_id = u.contest_id其中r.contest_id = 3;
二是如何保存這樣的對象？
cuser = ContestUser.objects.get(user_id = 1, contest_id = 1)
cuser.username = 'username'
cuser.save()
這導致IntegrityError：（1062， 「關鍵 '主要' 重複條目 '1-1'」）
執行的SQL是：
SELECT * FROM `users` WHERE (`users`.`contest_id` = 1 AND `users`.`user_id` = 1);
SELECT (1) AS `a` FROM `users` WHERE `users`.`user_id` = 1 LIMIT 1;
UPDATE `users` SET ... WHERE `users`.`user_id` = 1 ;