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具有2个外键选项的休眠实体

[英]Hibernate Entity with 2 foreign key options

原文 2018-06-06 08:15:56 6 1 java/ sql/ hibernate/ jpa

I have that use case: 我有那个用例：

I have table A and table B (none of them is extending the other, they are logically different). 我有表A和表B （它们都没有扩展另一个，它们在逻辑上是不同的）。 Both tables should have a link with one or more 'documents' . 两个表都应具有一个或多个“文档”的链接。 So I can design table A and table B, but how to design the table for the 'documents'? 因此，我可以设计表A和表B，但是如何为“文档”设计表呢？ Should it have 2 foreign key constraints (there is a possibilite one record from documents to have only 1 foreign key to Table A or B and the other foreign key will be null)? 它应该有2个外键约束吗（文档中有一个记录可能只对表A或B有1个外键，而另一个外键将为空）？ How I will declare that in SQL and in Hibernate/JPA. 我将如何在SQL和Hibernate / JPA中声明这一点。 Thanks in advance. 提前致谢。

1 个解决方案

You can have one-to-many unidirectional relationship from Table A/B to documents. 从表A / B到文档，您可以具有一对多的单向关系。 By doing so, you will require link tables between Table A/B and document (in other words, document will be a master table). 这样，您将需要在表A / B和文档之间建立链接表（换句话说，文档将是主表）。 Also you will require to store document separately first and then can assign the documents to the Table A/B entities. 另外，您将需要先单独存储文档，然后才能将文档分配给Table A / B实体。

Alternatively, if want to save the documents along with Table A/B entity, then you need to maintain both foreign keys which will be nullable ie either A or B. 或者，如果要将文档与表A / B实体一起保存，则需要维护两个可以为空的外键，即A或B。

Both approaches are fine hence depending on your business requirement you should pick one. 两种方法都很好，因此应根据您的业务需求选择一种。