@MappedSuperclass不是JPA中的@Entity吗? [英] @MappedSuperclass is not an @Entity in JPA?

问题描述

因此，我正在使用DerbyDB，并且正在设置一些实体.我有一个@MappedSuperclass，它用作某些实体(@Entity)的超类.更具体地说，我有一个超类User和3个子类，分别是admin，regular和guest.现在，我有一个不同的实体，假设file应该引用其所有者(作为其字段之一).因此，我创建了一个名为User owner的字段. 我得到的错误是:

So I am using DerbyDB and I am setting up some entities. I have a @MappedSuperclass which is used as a superclass for some entities (@Entity). More specifically, I have a superclass User and 3 subclasses namely admin, regular and guest. Now I have a different entity, let's say file that should reference (as one of its fields) its owner. So I created a field called User owner. The error I get is:

Exception Description: [File] uses a non-entity [User] as target entity in the relationship attribute [field owner].

有解决方法吗?

推荐答案

我可以提出两种解决方案:

I can suggest two solutions:

您得到的异常清楚地描述了您的问题:User不是实体.任何用接口@MappedSuperclass声明为超类的类都不能是实体(在标准JPA中-取决于您的JPA提供者) ...让我指出我刚刚给一个答案的答案.相似的问题

The exception you get clearly describes your problem: User is not an entity. Any class declared as superclass with the interface @MappedSuperclass cannot be an entity (in standard JPA - depends on your JPA-provider)... let me point you to an answer I just gave to quite a similar problem

-> 超类类型

因此，您描述了将超类定义为抽象实体将为您提供所需的行为.

So defining your superclass as an abstract entity will give you the desired behaviour, you described.

如果您将继承映射策略选择为@Inheritance(strategy = InheritanceType.SINGLE_TABLE)，则甚至不需要多个数据库表.这是一个很好的示例: JPA单表继承

If you choose your inheritance mapping strategy as @Inheritance(strategy = InheritanceType.SINGLE_TABLE) you don't even need multiple database-tables. Here is a good example: JPA Single-Table Inheritance

不要仅根据用户角色将其分成几个实体.制作一个具有所有所需角色的Enum并将其作为字段添加到您的User-实体.除非您需要您的管理员，来宾等成为自己的对象，否则这种情况普遍存在.

Don't split your user entity in several entities just by their roles. Make an Enum with all your desired roles and add it as a field to your User-entity. This is widely more common, unless u need your admin, guests etc to be an own object...

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