在OneToMany和ManyToMany映射中获取StackOverflow

Question

[当我尝试执行以下代码时，我得到了StackOverflow异常

@Test
public void testMappings() {
    EntityManager em = factory.createEntityManager();
    Query q = em.createQuery("select f from Student f");
    System.out.println(q.getResultList());
    em.close();
}

我有三个实体（Student，Course，CourseRegistration），如下所示

Student.java

@Entity
@Table(name = "student")
@Data
@EqualsAndHashCode
public class Student {

    @Id
    @Column(name = "id")
    private Long id;

    @Column(name = "name")
    private String name;

    @ManyToMany
    @JoinTable(name = "course_registration", joinColumns = @JoinColumn(name = "student_id"), inverseJoinColumns = @JoinColumn(name = "course_id"))
    private Set<Course> likedCourses;

    @OneToMany(mappedBy = "student")
    private Set<CourseRegistration> registrations;

    public Student() {
    }
}

Course.java

@Entity
@Table(name = "course")
@Data
@EqualsAndHashCode
public class Course {

    @Id
    @Column(name = "id")
    private Long id;

    @Column(name = "name")
    private String name;

    @ManyToMany(mappedBy = "likedCourses")
    private Set<Student> likes;

    @OneToMany(mappedBy = "course")
    private Set<CourseRegistration> registrations;

    public Course() {
    }
}

CourseRegistration.java

@Entity
@Table(name = "course_registration")
@Data
@EqualsAndHashCode
public class CourseRegistration {

    @Id
    @Column(name = "id")
    private Long id;

    @ManyToOne
    @MapsId("student_id")
    @JoinColumn(name = "student_id")
    private Student student;

    @ManyToOne
    @MapsId("course_id")
    @JoinColumn(name = "course_id")
    private Course course;

    @Column(name = "rating")
    private int rating;

    public CourseRegistration() {
    }
}

例外情况如下

java.lang.StackOverflowError
    at org.jboss.logging.Log4jLogger.doLog(Log4jLogger.java:40)
    at org.jboss.logging.Logger.debug(Logger.java:385)
    at org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:109)
    at org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:94)
    at org.hibernate.engine.jdbc.internal.StatementPreparerImpl$StatementPreparationTemplate.prepareStatement(StatementPreparerImpl.java:181)
    at org.hibernate.engine.jdbc.internal.StatementPreparerImpl.prepareQueryStatement(StatementPreparerImpl.java:160)
    at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.prepareQueryStatement(AbstractLoadPlanBasedLoader.java:257)
    at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeQueryStatement(AbstractLoadPlanBasedLoader.java:201)
    at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad(AbstractLoadPlanBasedLoader.java:137)
    at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad(AbstractLoadPlanBasedLoader.java:102)
    at org.hibernate.loader.collection.plan.AbstractLoadPlanBasedCollectionInitializer.initialize(AbstractLoadPlanBasedCollectionInitializer.java:100)
    at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:693)
    at org.hibernate.event.internal.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:92)
    at org.hibernate.internal.SessionImpl.initializeCollection(SessionImpl.java:1933)
    at org.hibernate.collection.internal.AbstractPersistentCollection$4.doWork(AbstractPersistentCollection.java:558)

谁能告诉我我哪里出了问题

https://github.com/alexman31/jpatest/中提供了完整的源代码

Answer 1

我建立了您的代码，发现此问题是由于lombok生成的hashCode()/equeals()和toString()方法引起的>>

        at model.Student.hashCode(Student.java:13)
        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 model.Course.hashCode(Course.java:13)
        at java.util.HashMap.hash(HashMap.java:339)
        at java.util.HashMap.put(HashMap.java:612)
        at java.util.HashSet.add(HashSet.java:220)
我已经删除了所有的龙目岛注释

（在数据库中添加了等级字段，结果是：

[Student{id=123, name='Manu', likedCourses=[Course{id=224, name='Course2'}, Course{id=223, name='Course1'}], registrations=[CourseRegistration{id=1, rating=1}, CourseRegistration{id=2, rating=1}]}, Student{id=124, name='Susan', likedCourses=[Course{id=223, name='Course1'}], registrations=[CourseRegistration{id=3, rating=1}]}, Student{id=125, name='Jacob', likedCourses=[Course{id=224, name='Course2'}, Course{id=223, name='Course1'}], registrations=[CourseRegistration{id=4, rating=1}, CourseRegistration{id=5, rating=1}]}, Student{id=126, name='Mathew', likedCourses=[Course{id=224, name='Course2'}, Course{id=223, name='Course1'}, Course{id=226, name='Course4'}], registrations=[CourseRegistration{id=6, rating=1}, CourseRegistration{id=8, rating=1}, CourseRegistration{id=7, rating=1}]}, Student{id=127, name='Sunny', likedCourses=[], registrations=[]}]

Answer 2

您是否研究过实体的已编译类？我的意思是lombok为您生成的那些equals（）