java-通过Hibernate保存实体时org.hibernate.WrongClassException

在这个问题中,我正在使用Hibernate 4.3.4.Final和Spring ORM 4.1.2.RELEASE.

我有一个User类,它拥有如下的CardInstances集：

@Entity
@Table
public class User implements UserDetails {

    protected List<CardInstance> cards;

    @ManyToMany
    public List<CardInstance> getCards() {
        return cards;
    }

    // setter and other members/methods omitted 
}

@Table
@Entity
@Inheritance
@DiscriminatorColumn(name = "card_type", discriminatorType = DiscriminatorType.STRING)
public abstract class CardInstance<T extends Card> {

    private T card;

    @ManyToOne
    public T getCard() {
        return card;
    }
}

@Table
@Entity
@Inheritance
@DiscriminatorOptions(force = true)
@DiscriminatorColumn(name = "card_type", discriminatorType = DiscriminatorType.STRING)
public abstract class Card {
    // nothing interesting here
}

我有几种类型的卡,每种类型分别扩展了Card基类和CardInstance基类,如下所示：

@Entity
@DiscriminatorValue("unit")
public class UnitCardInstance extends CardInstance<UnitCard> {
    // all types of CardInstances extend only the CardInstance<T> class
}

@Entity
@DiscriminatorValue("leader")
public class LeaderCardInstance extends CardInstance<LeaderCard> {

}

@Entity
@DiscriminatorValue("unit")
public class UnitCard extends Card {
}

@Entity
@DiscriminatorValue("leader")
public class LeaderCard extends AbilityCard {
}

@Entity
@DiscriminatorValue("hero")
public class HeroCard extends UnitCard {
    // card classes (you could call them the definitions of cards) can
    // extend other types of cards, not only the base class
}

@Entity
@DiscriminatorValue("ability")
public class AbilityCard extends Card {
}

如果我将UnitCardInstance或HeroCardInstance添加到纸牌集合并保存实体,则一切正常.
但是,如果我将AbilityCardInstance添加到集合中并保存该实体,它将失败,并出现org.hibernate.WrongClassException.我在帖子底部添加了确切的异常消息.

我通读了一些问题,在处理基类的集合时,延迟加载似乎是一个问题,因此这是我在添加卡并保存之前加载User实体的方式：

User user = this.entityManager.createQuery("FROM User u " +
                "WHERE u.id = ?1", User.class)
                .setParameter(1, id)
                .getSingleResult();

        Hibernate.initialize(user.getCards());

        return user;

“卡片”的数据库条目

“ cardinstances”的数据库条目

org.hibernate.WrongClassException: Object [id=1] was not of the specified subclass [org.gwentonline.model.cards.UnitCard] : Discriminator: leader

在此先感谢您提供任何线索来解决此问题.如果您需要其他信息,我们将很乐意更新我的问题！

解决方法:

根据first paragraph of the JavaDocs for @ManyToOne：

It is not normally necessary to specify the target entity explicitly since it can usually be inferred from the type of the object being referenced.

但是,在这种情况下,@ ManyToOne位于类型为泛型的字段上,并且泛型类型信息在编译类型时被擦除.因此,在反序列化时,Hibernate不知道该字段的确切类型.

解决方法是将targetEntity = Card.class添加到@ManyToOne.由于Card是抽象的,并且具有@Inheritance和@DiscriminatorColumn批注,因此这迫使Hibernate通过所有可能的方式解析实际的字段类型.它使用Card表的鉴别值执行此操作,并生成正确的类实例.此外,Java代码中保留了类型安全性.

因此,通常,只要在运行时可能无法完全了解字段的类型,就可以将targetEntity与@ManyToOne和@OneToMany一起使用.

标签：java,spring,jpa,hibernate,spring-orm
来源： https://codeday.me/bug/20191012/1898101.html