JPA如何处理部分的、非不相交的继承(在每个表的类场景中使用InheritanceType.JOINED)以及EntityManager.find()?

部分 非不相交的 带有JPA注释的继承。

这是四张桌子:

CREATE TABLE Persons (
  id INTEGER NOT NULL,
  first_name VARCHAR(50) NOT NULL,
  last_name VARCHAR(50) NOT NULL,
  PRIMARY KEY (id));

CREATE TABLE Referees (
  id INTEGER NOT NULL,
  license_nbr VARCHAR(10) DEFAULT NULL NULL,
  PRIMARY KEY (id),
  CONSTRAINT referees_persons_fk
    FOREIGN KEY (id)
    REFERENCES Persons (id)
    ON DELETE CASCADE
    ON UPDATE CASCADE);

CREATE TABLE Coaches (
  id INTEGER NOT NULL,
  license_nbr VARCHAR(10) DEFAULT NULL NULL,
  PRIMARY KEY (id),
  CONSTRAINT coaches_persons_fk
    FOREIGN KEY (id)
    REFERENCES Persons (id)
    ON DELETE CASCADE
    ON UPDATE CASCADE);

CREATE TABLE Players (
  id INTEGER NOT NULL,
  registration_nbr VARCHAR(20) DEFAULT NULL NULL,
  PRIMARY KEY (id),
  CONSTRAINT players_persons_fk
    FOREIGN KEY (id)
    REFERENCES Persons (id)
    ON DELETE CASCADE
    ON UPDATE CASCADE);

我缩短的实体类是:

@Entity
@Table(name = "Persons")
@Inheritance(strategy = InheritanceType.JOINED)
public class Person implements Serializable
{
    @Id
    @Column(name = "id")
    private Integer id;

    @Column(name = "first_name")
    private String firstName;

    @Column(name = "last_name")
    private String lastName;

    ...
}

@Entity
@Table(name = "Referees")
public class Referee extends Person implements Serializable
{
    @Column(name = "license_nbr")
    private String licenseNbr = null;

    ...
}

@Entity
@Table(name = "Coaches")
public class Coach extends Person implements Serializable
{
    @Column(name = "license_nbr")
    private String licenseNbr = null;

    ...
}

@Entity
@Table(name = "Players")
public class Player extends Person implements Serializable
{
    @Column(name = "registration_nbr")
    private String registrationNbr = null;

    ...
}

部分继承:人实体可以在没有任何相应的裁判、教练或球员实体的情况下存在。

注意,因为继承是部分的,所以Person不是抽象的。此外,由于继承是非分离的,因此对Person/s没有歧视。

这样的模型在Java ORMs中可能吗?注释看起来怎么样?

// Michael Jordan: the person who's only a player, too

// EclipseLink 2.1.1 ( 1): ?
// EclipseLink 2.2.0 ( 1): ?
// Hibernate 3.6     (-1): wrong Player instance
Person pe1 = em.find(Person.class, 1);
System.out.println("Loaded person = " + pe1);

// EclipseLink 2.1.1 ( 1): ?
// EclipseLink 2.2.0 ( 1): ?
// Hibernate 3.6     (+1): correct Player instance
Player pl1 = em.find(Player.class, 1);
System.out.println("Loaded player = " + pl1);

// EclipseLink 2.1.1 ( 1): ?
// EclipseLink 2.2.0 ( 1): ?
// Hibernate 3.6     (+1): correct null
Referee re1 = em.find(Referee.class, 1);
System.out.println("Loaded referee = " + re1);

// EclipseLink 2.1.1 ( 1): ?
// EclipseLink 2.2.0 ( 1): ?
// Hibernate 3.6     (+1): correct null
Coach ch1 = em.find(Coach.class, 1);
System.out.println("Loaded coach = " + ch1);

System.out.println();
System.out.println();

// Dirk Nowitzki: the person who's also a player *and* a referee

// EclipseLink 2.1.1 ( 1): ?
// EclipseLink 2.2.0 ( 1): ?
// Hibernate 3.6     (-1): wrong Player instance
Person pe2 = em.find(Person.class, 2);
System.out.println("Loaded person = " + pe2);

// EclipseLink 2.1.1 ( 1): ?
// EclipseLink 2.2.0 ( 1): ?
// Hibernate 3.6     (+1): correct Player instance
Player pl2 = em.find(Player.class, 2);
System.out.println("Loaded player = " + pl2);

// EclipseLink 2.1.1 ( 1): ?
// EclipseLink 2.2.0 ( 1): ?
// Hibernate 3.6     (-1): wrong null
Referee re2 = em.find(Referee.class, 2);
System.out.println("Loaded referee = " + re2);

// EclipseLink 2.1.1 ( 1): ?
// EclipseLink 2.2.0 ( 1): ?
// Hibernate 3.6     (+1): correct null
Coach ch2 = em.find(Coach.class, 2);
System.out.println("Loaded coach = " + ch2);

System.out.println();
System.out.println();

// Blake Griffin: the person who's also a player, referee, *and* coach

// EclipseLink 2.1.1 ( 1): ?
// EclipseLink 2.2.0 ( 1): ?
// Hibernate 3.6     (-1): wrong Player instance
Person pe3 = em.find(Person.class, 3);
System.out.println("Loaded person = " + pe3);

// EclipseLink 2.1.1 ( 1): ?
// EclipseLink 2.2.0 ( 1): ?
// Hibernate 3.6     (+1): correct Player instance
Player pl3 = em.find(Player.class, 3);
System.out.println("Loaded player = " + pl3);

// EclipseLink 2.1.1 ( 1): ?
// EclipseLink 2.2.0 ( 1): ?
// Hibernate 3.6     (-1): wrong null
Referee re3 = em.find(Referee.class, 3);
System.out.println("Loaded referee = " + re3);

// EclipseLink 2.1.1 ( 1): ?
// EclipseLink 2.2.0 ( 1): ?
// Hibernate 3.6     (-1): wrong null
Coach ch3 = em.find(Coach.class, 3);
System.out.println("Loaded coach = " + ch3);

EclipseLink 2.1.1和2.2.0夜间构建在EntityManager.find(…)上完全失败,而Hibernate至少返回一些预期的实例。注意这个词“ 预期 “这里。这是我对JPA ORM应该做什么的理解,但我可能错了。

如您所见,Hibernate总是返回Player的子类实例,但如果Player实例也可用,则无法找到Coach和jurier实例。