Hibernate双向映射
今天查阅了些关于Hibernate一对多映射的文章，基本可以总结为：将多端设置为主控方（inverse = false），可以优化性能。网上形象的比喻是，如果要让国家领导人记住全国人民的名字，估计花个几十年也不可能，但要让全国人民知道国家领导人，可就不需要那么多时间了。
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又见Hibernate官方annotations文档关于双向映射的描述：
Since many to one are (almost) always the owner side of a bidirectional relationship in the JPA spec, the one to many association is annotated by @OneToMany(mappedBy=...)
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将one to many端声明 mappedBy，便等价于将多端设置为 主控方 。
To map a bidirectional one to many, with the one-to-many side as the owning side, you have to remove the mappedBy element and set the many to one @JoinColumn as insertable and updatable to false. This solution is not optimized and will produce some additional UPDATE statements.
如果去掉 mappedBy元素，并在 many to one端设置 insertable和 updatable为false， one-to-many将做为主控方，但这样将产生多余的update语句不能达到优化的目的。
