含@Any注解的Hibernate Entity更新时抛出NullPointerException

问题根源 #

你遇到的空指针异常是因为GameScore类中@Any注解的配置错误：错误使用@JoinColumn来指定关联外键列，这种配置不符合Hibernate对@Any注解的解析要求，导致更新操作时Hibernate无法正确识别属性映射，进而抛出空指针。

正确配置方式 #

修正GameScore中player字段的注解，用@Column分别指定鉴别列和外键列，移除错误的@JoinColumn，或者直接通过@Any注解的属性来定义这两个列。

修正后的GameScore代码 #

package com.example.demo;

import jakarta.persistence.*;
import org.hibernate.annotations.Any;
import org.hibernate.annotations.AnyDiscriminator;
import org.hibernate.annotations.AnyDiscriminatorValue;
import org.hibernate.annotations.AnyKeyJavaClass;

@Entity
public class GameScore  {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Any
    @AnyDiscriminator(DiscriminatorType.STRING)
    @AnyDiscriminatorValue(discriminator = "P", entity = PcPlayer.class)
    @AnyDiscriminatorValue(discriminator = "C", entity = ConsolePlayer.class)
    @AnyKeyJavaClass(Long.class)
    @Column(name = "player_type") // 存储玩家类型的鉴别列
    @Column(name = "player_id")   // 存储玩家ID的外键列
    private Player player;

    // Getter & Setter
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }
    public Player getPlayer() { return player; }
    public void setPlayer(Player player) { this.player = player; }
}

或者更简洁的写法（推荐）：

@Any(
    discriminatorColumn = @Column(name = "player_type"),
    keyColumn = @Column(name = "player_id")
)
@AnyDiscriminator(DiscriminatorType.STRING)
@AnyDiscriminatorValue(discriminator = "P", entity = PcPlayer.class)
@AnyDiscriminatorValue(discriminator = "C", entity = ConsolePlayer.class)
@AnyKeyJavaClass(Long.class)
private Player player;

关键注意点 #

1. 数据库表game_score必须包含player_type（字符串类型）和player_id（长整型）两个字段，不需要建立数据库外键约束，因为@Any是逻辑层面的多态关联。
2. 更新操作前，确保GameScore实例的player属性处于持久态或被正确加载，避免游离态实体引发的映射问题。
3. 如果你使用的是Hibernate 6.x版本，部分注解属性可能有调整，可参考对应版本的官方文档确认细节。

内容的提问来源于stack exchange，提问作者RasAlGhul