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阿里巴巴的Java开发手册中有这样一句话:
不得使用外键与级联,一切外键概念必须在应用层解决!
以student和grade的关系为例 ,student中的student_id是主键,成绩表中的student_id则为外键 !
先了解一下什么叫级联更新和级联删除!
当在student表中要删除或者更新student_id=20的相关信息,马上在grade表中中查找是否有student_id=20
这个记录,然后进行删除或更新,这就叫级联。
外键和级联比较适合单机和低并发
的情况下 ,但大量的事物无疑会造成很多问题,比如说高并发下的死锁,大量事物也会影响crun速度,不适合分布式和高并发集群。应该写一层功能来保证,然后应用通过这一层功能来访问数据库。
不使用外键约束的优缺点:
1.不使用外键牺牲了数据库中数据的一致性,但是却能够减少数据库的负载;
2.数据管理简单,操作方便,性能高;
3.应用层的逻辑无疑会增加我们的代码量和维护;
最后,外键约束到底使用不使用:
这取决于我们的项目的开发需求以及数据库的选择,根据实际需求和情况,来考虑使用不使用外键约束以及外键约束的选取,这些都是需要衡量的!