Java 为什么GAE上Datanucleus JDO的继承深度很重要？ 如果我有一个继承级别，则所有内容都会按预期在App Engine中持久化：

Worker.java

import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.Inheritance;
import javax.jdo.annotations.InheritanceStrategy;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;

@PersistenceCapable
@Inheritance(strategy = InheritanceStrategy.SUBCLASS_TABLE)
public abstract class Worker {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key key;

    @Persistent
    private String department;
}

@PersistenceCapable
@Inheritance(strategy = InheritanceStrategy.SUBCLASS_TABLE)
public abstract class Worker extends Human {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key key;

    @Persistent
    private String department;
}

Employee.java

// ... imports ...

@PersistenceCapable
public class Employee extends Worker {
    @Persistent
    private int salary;

}

Intern.java

import java.util.Date;
// ... imports ...

@PersistenceCapable
public class Intern extends Worker {
    @Persistent
    private Date internshipEndDate;
}

但是，如果我添加一个额外的继承层，则最高级别子类中的字段不会持久化： Human.java

@PersistenceCapable
public abstract class Human {

    @Persistent
    private String name;
}

Worker.java

import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.Inheritance;
import javax.jdo.annotations.InheritanceStrategy;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;

@PersistenceCapable
@Inheritance(strategy = InheritanceStrategy.SUBCLASS_TABLE)
public abstract class Worker {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key key;

    @Persistent
    private String department;
}

@PersistenceCapable
@Inheritance(strategy = InheritanceStrategy.SUBCLASS_TABLE)
public abstract class Worker extends Human {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key key;

    @Persistent
    private String department;
}

---

为什么扩展抽象类可以，但让抽象类扩展更高级别的类不可以？并且您的主键现在不在（可持久的）继承树的根类中，因此JDO和JPA规范无效。

您还应该将以下声明移到人类类：

@Inheritance(strategy = InheritanceStrategy.SUBCLASS_TABLE)

---

按照您的建议，我将主键字段从Worker移到Human。现在，当我实例化一个雇员时，我得到了错误：

Exception:javax.jdo.JDOFatalUserException:com.foo.Employee上找到了继承策略“超类表”。此上下文不支持此策略。

因此请指定该类的继承策略！根据JDO规范