Java 将没有主键的 SQL 视图映射到 JPA 实体
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Mapping a SQL View with no Primary Key to JPA Entity
提问by user2144555
In my Java App I want to get information that is stored in my Oracle Database, using JPA. In my Database I have a View, with a set of columns that I got from some other tables. I want to map that View. However, my View doesn't have a Primary Key, so I can't create a JPA Entity. I thought about use 2 columns as Foreign Keys.
在我的 Java 应用程序中，我想使用 JPA 获取存储在我的 Oracle 数据库中的信息。在我的数据库中，我有一个视图，其中包含从其他一些表中获取的一组列。我想映射那个视图。但是，我的View 没有 Primary Key，因此我无法创建 JPA 实体。我想过使用 2 列作为外键。
What's the best way of implementing that? I've seen so many different approaches, that I can't decide which is the best for this case.
实现它的最佳方法是什么？我见过很多不同的方法，我无法决定哪种方法最适合这种情况。
采纳答案by PepperBob
One way to solve this is use a composite primary key by just adding the @Id annotation to the appropriate fields.
解决此问题的一种方法是通过将 @Id 注释添加到适当的字段来使用复合主键。
回答by Andrei I
There is no best approach. As that is a View, you will never insert any data in it, meaning you can simply define a Primary Key over any of existing fields. Also you could try to mark that field with insertable=false, updatable=false.
没有最好的方法。由于这是一个视图，您永远不会在其中插入任何数据，这意味着您可以简单地在任何现有字段上定义主键。您也可以尝试用insertable=false, updatable=false.
UPDATE
更新
You know better your data, but in generalin a view you cannot guarantee that all records are unique, which is why you should in generalavoid working directly with entities from the view. I would suggest rather working with a Wrapper class, something like:
您更了解您的数据，但通常在视图中您不能保证所有记录都是唯一的，这就是为什么您通常应该避免直接使用视图中的实体。我建议宁可使用 Wrapper 类，例如：
SELECT new com.domain.MyWrapper(field1, field2, field3, field4,...) FROM ViewEntity
