Hibernate 6单表继承类型识别异常：关联对象映射错误

问题背景 #

使用Hibernate 6.2.7.FINAL版本，该场景在Hibernate 5中可正常运行，现遇到继承类型无法识别的问题。

实体代码 #

基础实体类Animal #

@Entity
@Table(name = "ANIMAL")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "ANIMAL_TYPE")
@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type")
@JsonSubTypes({
  @Type(value = Giraffe.class, name = "giraffeAnimal"),
  @Type(value = Tiger.class, name = "tigerAnimal")
})
@org.hibernate.annotations.DiscriminatorOptions(force = true)
public class Animal {}

子类Tiger #

@Getter
@Setter
@NoArgsConstructor
@Entity
@DiscriminatorValue("Tiger")
public class Tiger extends Animal {}

子类Giraffe #

@Getter
@Setter
@NoArgsConstructor
@Entity
@DiscriminatorValue("Giraffe")
public class Giraffe extends Animal {}

Main实体类 #

@Entity
@Table(name = "MAIN")
public class Main {

  @OneToOne(cascade = CascadeType.ALL, mappedBy = "main")
  private Tiger tiger;

  @OneToMany(
    mappedBy = "main",
    cascade = {CascadeType.PERSIST, CascadeType.MERGE},
    orphanRemoval = true)
  private List<Giraffe> girrafes;
}

问题现象与异常 #

当持久化包含1个Giraffe对象、无Tiger对象的Main类实例到数据库时，Animal表中数据正确，ANIMAL_TYPE鉴别器列值为Giraffe；但从数据库查询Main对象时，同一个Giraffe对象同时出现在Tiger属性和Giraffe列表中，而Tiger属性应为null。

集成测试抛出异常：

Caused by: org.hibernate.PropertyAccessException: 无法为类型[com.example.Girraffe]设置值: 'com.example.Main.Tiger'（setter方法）    
at org.hibernate.property.access.spi.SetterFieldImpl.set(SetterFieldImpl.java:88)   
at org.hibernate.property.access.spi.EnhancedSetterImpl.set(EnhancedSetterImpl.java:42)     
at org.hibernate.persister.entity.AbstractEntityPersister.setPropertyValues(AbstractEntityPersister.java:4398)  
at org.hibernate.sql.results.graph.entity.AbstractEntityInitializer.initializeEntityInstance(AbstractEntityInitializer.java:851)    
at org.hibernate.sql.results.graph.entity.AbstractEntityInitializer.initializeEntity(AbstractEntityInitializer.java:811)    
at org.hibernate.sql.results.graph.entity.AbstractEntityInitializer.initializeInstance(AbstractEntityInitializer.java:797)  
at org.hibernate.sql.results.internal.InitializersList.initializeInstance(InitializersList.java:71)     
at org.hibernate.sql.results.internal.StandardRowReader.coordinateInitializers(StandardRowReader.java:109)  
at org.hibernate.sql.results.internal.StandardRowReader.readRow(StandardRowReader.java:86)  
at org.hibernate.sql.results.spi.ListResultsConsumer.consume(ListResultsConsumer.java:181)  
at org.hibernate.sql.results.spi.ListResultsConsumer.consume(ListResultsConsumer.java:33)   
at org.hibernate.sql.exec.internal.JdbcSelectExecutorStandardImpl.doExecuteQuery(JdbcSelectExecutorStandardImpl.java:361)   
at org.hibernate.sql.exec.internal.JdbcSelectExecutorStandardImpl.executeQuery(JdbcSelectExecutorStandardImpl.java:168)     
at org.hibernate.sql.exec.internal.JdbcSelectExecutorStandardImpl.list(JdbcSelectExecutorStandardImpl.java:93)  
at org.hibernate.sql.exec.spi.JdbcSelectExecutor.list(JdbcSelectExecutor.java:31)   
at org.hibernate.query.sqm.internal.ConcreteSqmSelectQueryPlan.lambda$new$0(ConcreteSqmSelectQueryPlan.java:109)    
at org.hibernate.query.sqm.internal.ConcreteSqmSelectQueryPlan.withCacheableSqmInterpretation(ConcreteSqmSelectQueryPlan.java:305)  
at org.hibernate.query.sqm.internal.ConcreteSqmSelectQueryPlan.performList(ConcreteSqmSelectQueryPlan.java:246)     
at org.hibernate.query.sqm.internal.QuerySqmImpl.doList(QuerySqmImpl.java:509)  
at org.hibernate.query.spi.AbstractSelectionQuery.list(AbstractSelectionQuery.java:427)     
at org.hibernate.query.spi.AbstractSelectionQuery.getSingleResult(AbstractSelectionQuery.java:559)

解决方案 #

该问题源于Hibernate 6处理单表继承关联映射时，未自动依据鉴别器值过滤关联实体类型，导致尝试将Giraffe实例赋值给Tiger属性，触发类型不匹配异常。直接有效的解决方式是在关联注解上显式添加鉴别器过滤条件：

1. 为@OneToOne的Tiger属性添加@Where注解指定鉴别器值：

@OneToOne(cascade = CascadeType.ALL, mappedBy = "main")
@Where(clause = "ANIMAL_TYPE = 'Tiger'")
private Tiger tiger;

2. 为@OneToMany的Giraffe列表添加@Where注解：

@OneToMany(
  mappedBy = "main",
  cascade = {CascadeType.PERSIST, CascadeType.MERGE},
  orphanRemoval = true)
@Where(clause = "ANIMAL_TYPE = 'Giraffe'")
private List<Giraffe> girrafes;

同时需检查Animal子类中mappedBy指定的main关联字段是否正确定义，确保每个子类都有对应类型的Main关联属性。

内容的提问来源于stack exchange，提问作者Mohd Salim