跨数据库加入JPA [英] Cross database joins in JPA

问题描述

是否可以在JPA中执行交叉数据库表连接？

Is it possible to do cross database table joins in JPA?

我在一个数据库中有一个 users 表，其中有一个组织的外键在单独的数据库中。这两个数据库都在同一物理机器上。现在MySQL允许我写跨越多个数据库的查询，但我不知道如何用JPA这样做。

I have a users table in one database which has a foreign key to a organizations table in a separate database. Both the databases are on same physical machine. Now MySQL allows me to write queries which span across multiple databases, but I am not sure how to do this with JPA.

@Entity Java POJO的注释没有使用数据库的名称，因此没有办法标记交叉数据库关系。

The @Entity annotations on the Java POJO's don't take the name of the database so there is no way to mark a cross DB relationship.

这种情况的解决方法？也许使用本机查询来加载已加入的实体？

Is there a workaround for this situation? Perhaps using a native query to load the joined entity?

推荐答案

我们尝试了以下方法，似乎工作。

We tried out the following approach and seems to work.

1）@Table注释中没有架构属性

1) No schema attribute in the @Table annotations

2）为实体创建不同的orm文件它们所在的模式。

2) create different orm files for entities clubbed by the schema in which they are present.

3）在每个orm文件中，您可以添加my_schema。

3) In each of the orm files, you can add a "my_schema".

4）在你的相应的PU中的orm文件在persistence.xml

4) Include the orm files in your respective PUs in the persistence.xml

5）如果你想在测试期间不同的数据库，创建类似的orm文件测试和更改模式并将这些orm文件包含在单独的PU中

5) And if you want different databases during tests, create similar orm files for test and change the value in the schema accordingly and include these orm files in a separate PU

HTH

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