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
我使用的是 JPA2 并且 @Entity
和 @Table
都有一个 name
属性,例如.:
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?
在我的特定情况下,我有一个 User
类和一个 Group
类,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.
在编写查询时,一个有效的解决方案会是什么样子,我会用哪个名称来指代实体?
How would a working solution look like and with which name would I refer to the entity when writing queries?
更新:我在 Group
的两个注释中都添加了 name="GROUPS"
并对 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 {}
将创建名为MyEntity"的表,实体名称将为 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,您总是使用实体名称,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 {}
然后创建一个名为 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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