Hibernate @ManyToMany 坚持

Question

我对 @ManyToMany 关系有疑问。

我有一个实体 Category 在数据库中有预定义的插入。

我有实体 Trigger，它必须包含预定义的 Category :

@Entity
@Data
public class Category {

    @Id
    private Long id;

    private String name;

    @ManyToMany(cascade = CascadeType.ALL, mappedBy = "categories")
    private Set<Trigger> trigger;

@Entity
@Data
public class Trigger {

    @ManyToMany()
    private Set<Category> categories;
}



Trigger trigger = new Trigger();
trigger.setName(triggerDTO.getName());
trigger.setCategories(triggerDTO.getCategories()
            .stream()
            .map(c -> categoryRepository.findByName(c.getName()))
            .collect(Collectors.toSet()));

所以当我坚持第一个 Trigger 时一切都很好，但是当我尝试坚持下一个 Trigger 时，我看到：

java.lang.WhosebugError: null
  at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:401) ~[postgresql-42.2.23.jar:42.2.23]
  at org.postgresql.jdbc.PgPreparedStatement.executeWithFlags(PgPreparedStatement.java:164) ~[postgresql-42.2.23.jar:42.2.23]
  at org.postgresql.jdbc.PgPreparedStatement.executeQuery(PgPreparedStatement.java:114) ~[postgresql-42.2.23.jar:42.2.23]
  at com.zaxxer.hikari.pool.ProxyPreparedStatement.executeQuery(ProxyPreparedStatement.java:52) ~[HikariCP-4.0.3.jar:na]
  at com.zaxxer.hikari.pool.HikariProxyPreparedStatement.executeQuery(HikariProxyPreparedStatement.java) ~[HikariCP-4.0.3.jar:na]
  at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:57) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.getResultSet(AbstractLoadPlanBasedLoader.java:390) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeQueryStatement(AbstractLoadPlanBasedLoader.java:163) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad(AbstractLoadPlanBasedLoader.java:104) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.loader.collection.plan.AbstractLoadPlanBasedCollectionInitializer.initialize(AbstractLoadPlanBasedCollectionInitializer.java:87) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:710) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.event.internal.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:76) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:99) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.internal.SessionImpl.initializeCollection(SessionImpl.java:2163) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.collection.internal.AbstractPersistentCollection.doWork(AbstractPersistentCollection.java:589) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:264) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:585) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:149) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.collection.internal.PersistentSet.hashCode(PersistentSet.java:458) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at com.myapp.domain.trigger.Trigger.hashCode(Trigger.java:13) ~[classes/:na]
  at java.base/java.util.HashMap.hash(HashMap.java:340) ~[na:na]
  at java.base/java.util.HashMap.put(HashMap.java:612) ~[na:na]
  at java.base/java.util.HashSet.add(HashSet.java:221) ~[na:na]
  at java.base/java.util.AbstractCollection.addAll(AbstractCollection.java:336) ~[na:na]
  at org.hibernate.collection.internal.PersistentSet.endRead(PersistentSet.java:355) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.engine.loading.internal.CollectionLoadContext.endLoadingCollection(CollectionLoadContext.java:239) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.engine.loading.internal.CollectionLoadContext.endLoadingCollections(CollectionLoadContext.java:224) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.engine.loading.internal.CollectionLoadContext.endLoadingCollections(CollectionLoadContext.java:198) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.loader.plan.exec.process.internal.CollectionReferenceInitializerImpl.endLoading(CollectionReferenceInitializerImpl.java:154) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.loader.plan.exec.process.internal.AbstractRowReader.finishLoadingCollections(AbstractRowReader.java:253) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.loader.plan.exec.process.internal.AbstractRowReader.finishUp(AbstractRowReader.java:211) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.loader.plan.exec.process.internal.ResultSetProcessorImpl.extractResults(ResultSetProcessorImpl.java:96) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad(AbstractLoadPlanBasedLoader.java:105) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.loader.collection.plan.AbstractLoadPlanBasedCollectionInitializer.initialize(AbstractLoadPlanBasedCollectionInitializer.java:87) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:710) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.event.internal.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:76) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:99) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.internal.SessionImpl.initializeCollection(SessionImpl.java:2163) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.collection.internal.AbstractPersistentCollection.doWork(AbstractPersistentCollection.java:589) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:264) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:585) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:149) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at org.hibernate.collection.internal.PersistentSet.hashCode(PersistentSet.java:458) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
  at com.myapp.domain.trigger.observation.component.Category.hashCode(Category.java:10) ~[classes/:na]
  at java.base/java.util.HashMap.hash(HashMap.java:340) ~[na:na]
  at java.base/java.util.HashMap.put(HashMap.java:612) ~[na:na]
  at java.base/java.util.HashSet.add(HashSet.java:221) ~[na:na]

如果将设置更改为列表，工作正常，为什么？

Answer 1

简明扼要：使用

@NoArgsConstructor
@Getter

足以满足 serializing/deserializing 而不是您当前的 @Data

它对 Set 不起作用的原因是 @EqualsAndHashCode 在您的 @Data.

在这里，每次插入 Trigger 时，JPA 首先获取您的 Trigger 及其依赖项 Category。例如，您有 1 Trigger 和 1 Category

select
    trigger0_.id as id1_1_0_ 
from
    trigger trigger0_ 
where
    trigger0_.id=?

select
    category0_.id as id1_0_0_,
    category0_.name as name2_0_0_ 
from
    category category0_ 
where
    category0_.id=?

并且因为您将 Set<Trigger> 放在 Category class 中，所以此 Trigger 的哈希码将使用 Lombok @EqualsAndHashCode 计算。这就是 JPA 需要加载此 Trigger 以便计算哈希码的原因

select
    trigger0_.categories_id as categori2_2_0_,
    trigger0_.trigger_id as trigger_1_2_0_,
    trigger1_.id as id1_1_1_ 
from
    trigger_categories trigger0_ 
inner join
    trigger trigger1_ 
        on trigger0_.trigger_id=trigger1_.id 
where
    trigger0_.categories_id=?

所以在你第一次插入的时候，没有Trigger，它可以很容易地计算出Category的哈希码，到这里就完成了

insert into trigger(id) values (?)
insert into trigger_categories(trigger_id, categories_id) values (?, ?)

但是第二次，如果你用之前的Category插入一个新的Trigger，这次之前的Category链接到之前的Trigger，所以计算hashCode时会出现循环

select
    trigger0_.categories_id as categori2_2_0_,
    trigger0_.trigger_id as trigger_1_2_0_,
    trigger1_.id as id1_1_1_ 
from
    trigger_categories trigger0_ 
inner join
    trigger trigger1_ 
        on trigger0_.trigger_id=trigger1_.id 
where
    trigger0_.categories_id=?

select
    categories0_.trigger_id as trigger_1_2_0_,
    categories0_.categories_id as categori2_2_0_,
    category1_.id as id1_0_1_,
    category1_.name as name2_0_1_ 
from
    trigger_categories categories0_ 
inner join
    category category1_ 
        on categories0_.categories_id=category1_.id 
where
    categories0_.trigger_id=?

如果要保留@EqualsAndHashCode，尽量忽略关系字段，例如

@NoArgsConstructor
@Getter
@EqualsAndHashCode(of = {"id"})

或者按你说的变成List

Hibernate @ManyToMany 坚持

Hibernate @ManyToMany persist

hibernate

spring-data-jpa

spring-data