使用 JPA 时，@Entity 和 @Table 中的 name 参数有什么区别? [英] What's the difference between the name argument in @Entity and @Table when using JPA?

问题描述

我正在使用 JPA2，并且 @Entity 和 @Table 都有一个 name 属性，例如.g.:

I'm using JPA2 and both @Entity and @Table have a name attribute, e. g.:

@Entity(name="Foo")
@Table (name="Bar")
class Baz

我应该使用什么，哪些是可选的?

What should I use, which ones are optional?

在我的具体情况下，我有一个类 User 和一个类 Group，它们有额外的要求(据我所知)，因为它们是 SQL 中的保留字.

In my specific case I have a class User and a class Group, which have additional requirements (as far as I understand) because they are reserved words in SQL.

一个可行的解决方案是什么样的?在编写查询时我将使用哪个名称来引用实体?

How would a working solution look like and with which name would I refer to the entity when writing queries?

更新:我将 name="GROUPS" 添加到 Group 的两个注释中，并为 User 做了同样的事情，但现在我明白了错误:

Update: I added name="GROUPS" to both annotations in Group and did the same for User, but now I get this error:

Exception Description: The table [USERS] is not present in this descriptor.
Descriptor: RelationalDescriptor(example.Group --> [DatabaseTable(GROUPS)])

还有这个错误

Internal Exception: java.sql.SQLException: Table not found in statement [SELECT ID, MAXIMUMROLE, MEMBERSHIPS_ID FROM USERS]

推荐答案

@Table 是可选的.将 POJO 类注释为实体时需要 @Entity，但 name 属性不是必需的.

@Table is optional. @Entity is needed for annotating a POJO class as an entity, but the name attribute is not mandatory.

如果你有课

 @Entity
 class MyEntity {}

将创建一个名为MyEntity"的表，实体名称为MyEntity.您的 JPQL 查询将是:

A table with name "MyEntity" will be created and the Entity name will be MyEntity. Your JPQL query would be:

 select * from MyEntity

在 JPQL 中，您始终使用实体名称，默认情况下它是类名称.

In JPQL you always use the Entity name and by default it is the class name.

如果你有课

 @Entity(name="MyEntityName")
 @Table(name="MyEntityTableName")
 class MyEntity {}

然后创建名称为 MyEntityTableName 的表，实体名称为 MyEntityName.

then a table with name MyEntityTableName is created and the entity name is MyEntityName.

您的 JPQL 查询将是:

Your JPQL query would be :

 select * from MyEntityName

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