使用hibernate / spring数据的三层实体映射会导致无限递归循环

Question

我遇到了一个问题。所以：我有五个实体，它们与其他实体有关系映射。这是这个结构的样子：

Relation diagram

Book.java实体

@JsonManagedReference
@OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL,mappedBy = "book")
private Set<Review> reviews = new HashSet<>();
@JsonManagedReference
@OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "book")
private Set<Comment> comments = new HashSet<>();

@ManyToOne(fetch = FetchType.EAGER, cascade = {CascadeType.MERGE,CascadeType.DETACH,
        CascadeType.PERSIST,CascadeType.REFRESH})
@JoinColumn(name = "author_last_name")
@JsonBackReference
private Author author;

Author.java实体：

    @JsonManagedReference
@OneToMany(fetch = FetchType.EAGER, cascade = {CascadeType.MERGE,
        CascadeType.DETACH,CascadeType.PERSIST,CascadeType.REFRESH},
        mappedBy = "author")
private Set<Book> books = new HashSet<>();

Review.java实体

@ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.DETACH,CascadeType.MERGE,CascadeType.PERSIST,CascadeType.REFRESH})
@JoinColumn(name = "book_id")
@JsonBackReference
private Book book;

Comment.java实体

@ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.DETACH,CascadeType.MERGE,
        CascadeType.PERSIST,CascadeType.REFRESH})
@JoinColumn(name = "book_id")
@JsonBackReference
private Book book;

在每个实体中，我都有getters / setter / hashCode等。还提供了向书籍或书籍添加评论的方法。

    public void addBookToAuthor(Book book){
    books.add(book);
    book.setAuthor(this);
}

问题是，我可以得到所有作者，获得单一作者等等，但是当我试图以这种方式为作者设置几本书时：

    public void shouldSaveAnAuthorAndSetBooks(){
        Author author = authorService.findAuthorByLastName("qwerty");
        HashSet<Book> books = new HashSet<>();
        books.add(bookService.findById(5));
        books.add(bookService.findById(8));
        books.add(bookService.findById(10));
        books.forEach(book -> author.addBookToAuthor(book));
        authorRepository.save(author);
}

它引导我进入无限循环，其中hibernate正在选择所有书籍/评论/评论：

Hibernate: select reviews0_.book_id as book_id5_4_0_, reviews0_.review_id as review_i1_4_0_, reviews0_.review_id as review_i1_4_1_, reviews0_.book_id as book_id5_4_1_, reviews0_.review as review2_4_1_, reviews0_.review_downvotes as review_d3_4_1_, reviews0_.review_upvotes as review_u4_4_1_ from review reviews0_ where reviews0_.book_id=?

这条线印刷1000次以上。然后显示1000多个关于故障安全清理的警告，最后以这种方式抛出StackOverFlowExc：

java.lang.StackOverflowError
at com.mysql.cj.NativeSession.execSQL(NativeSession.java:1220)
at com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:952)
at com.mysql.cj.jdbc.ClientPreparedStatement.executeQuery(ClientPreparedStatement.java:1025)
at com.zaxxer.hikari.pool.ProxyPreparedStatement.executeQuery(ProxyPreparedStatement.java:52)
at com.zaxxer.hikari.pool.HikariProxyPreparedStatement.executeQuery(HikariProxyPreparedStatement.java)
at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:60)
at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.getResultSet(AbstractLoadPlanBasedLoader.java:419)
at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeQueryStatement(AbstractLoadPlanBasedLoader.java:191)
at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad(AbstractLoadPlanBasedLoader.java:121)
at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad(AbstractLoadPlanBasedLoader.java:86)
at org.hibernate.loader.collection.plan.AbstractLoadPlanBasedCollectionInitializer.initialize(AbstractLoadPlanBasedCollectionInitializer.java:87)
at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:688)
at org.hibernate.event.internal.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:75)
at org.hibernate.internal.SessionImpl.initializeCollection(SessionImpl.java:2223)
at org.hibernate.collection.internal.AbstractPersistentCollection$4.doWork(AbstractPersistentCollection.java:565)
at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:247)
at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:561)
at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:132)
at org.hibernate.collection.internal.PersistentSet.hashCode(PersistentSet.java:430)
at java.util.Arrays.hashCode(Arrays.java:4146)
at java.util.Objects.hash(Objects.java:128)
at com.example.com.example.entity.Book.hashCode(Book.java:190)
at java.util.Arrays.hashCode(Arrays.java:4146)
at java.util.Objects.hash(Objects.java:128)
at com.example.com.example.entity.Review.hashCode(Review.java:93)
at java.util.HashMap.hash(HashMap.java:339)
at java.util.HashMap.put(HashMap.java:612)
at java.util.HashSet.add(HashSet.java:220)
at java.util.AbstractCollection.addAll(AbstractCollection.java:344)
at org.hibernate.collection.internal.PersistentSet.endRead(PersistentSet.java:327)

当然这个堆栈跟踪也是如此，循环显示。所以我的问题是：我该怎么办？我必须改变映射吗？还是保存的方法？

Answer 1

嗯，这个问题很简单。在书籍和评论实体上有一个覆盖HashCode方法的错误。所以道德是：不要使用HashSet或HashMap，让你的IDE为你生成哈希码。最好自己写