JPA ManyToMany映射问题（无法将同一实体映射到另一个实体）

Question

I'm new to jpa and spring-data , so please forgive my ignorance on the matter.

I have two Entities, and I'm having trouble mapping them to each other with ManyToMany relationship:

Department:

@Entity
@Table(name = "Department")
public class Department {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private Integer         id;

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

    @ManyToMany(fetch = FetchType.EAGER, cascade = { CascadeType.ALL })
    @JoinTable(name = "department_week_days", joinColumns = @JoinColumn(name = "department_id"), inverseJoinColumns = @JoinColumn(name = "week_day_id"))
    private List<WeekDay>   weekDays;

    public Department(String name) {
        this.name = name;
        weekDays = new ArrayList<WeekDay>();
    }

    protected Department() {
    }

    public void addWeekDay(WeekDay day) {
        weekDays.add(day);
        day.getDepartments().add(this);
    }

    // omitted setters and getters 

}

and

WeekDay:

@Entity
public class WeekDay {

    public static enum WeekDays {

        MO("Monday", 1), TU("Tuesday", 2), WE("Wednesday", 3), TH("Thursday ", 4), FR("Friday", 5), SA("Saturday", 6), SU("Sunday", 7);

        private String  name;
        private int     dayNum;

        private WeekDays(String name, int dayNum) {
            this.name = name;
            this.dayNum = dayNum;
        }

        public int asInt() {
            return dayNum;
        }

        @Override
        public String toString() {
            return name;
        }
    }

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private Integer             id;

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

    @Transient
    private int                 numericOrder;

    @Embedded
    private WorkingHours        workingHours;

    @Column(name = "minimumEmployees")
    private Integer             minimumEmployees;

    @Column(name = "maximumEmployees")
    private Integer             maximumEmployees;

    @ManyToMany(mappedBy = "weekDays")
    private List<Department>    departments;

    public WeekDay(WeekDays day, WorkingHours workingHours, Integer minimumEmployees, Integer maximumEmployees) {

        this.name = day.toString();
        this.numericOrder = day.asInt();
        this.workingHours = workingHours;
        this.minimumEmployees = minimumEmployees;
        this.maximumEmployees = maximumEmployees;

        departments = new ArrayList<Department>();

    }

    protected WeekDay() {
    }

    // omitted setters and getters

}

My problem is that I can't add the same WeekDay to two different Department 's for example:

WeekDay day = WeekDayFactory.create(WeekDayFactory.SA, WeekDayFactory.DAY_SHORT, 1, 2);

Department d1 = new Department("d1");
d1.addWeekDay(day);
repository.save(d1);

Department d2 = new Department("d2");
d2.addWeekDay(day);
repository.save(d2);

the above wont let me add day into d2 why?

If I create a new WeekDay with the same values as day it works:

WeekDay day = WeekDayFactory.create(WeekDayFactory.SA, WeekDayFactory.DAY_SHORT, 1, 2);
WeekDay sameValuesAsDay = WeekDayFactory.create(WeekDayFactory.SA, WeekDayFactory.DAY_SHORT, 1, 2);

Department d1 = new Department("d1");
d1.addWeekDay(day);
repository.save(d1);

Department d2 = new Department("d2");
d2.addWeekDay(sameValuesAsDay);
repository.save(d2);

obviously this creates a duplicate row in the WeekDay table which defeats the purpose of ManyToMany mapping since I can just add the data into the department table it self for each department .

As I said at the beginning, I have no real idea on how to do this correctly so please excuse my ignorance and point me in the right direction to solve my problem.

EDIT

stack trace:

java.lang.IllegalStateException: Failed to execute CommandLineRunner
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:735) [spring-boot-1.5.7.RELEASE.jar:1.5.7.RELEASE]
    at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:716) [spring-boot-1.5.7.RELEASE.jar:1.5.7.RELEASE]
    at org.springframework.boot.SpringApplication.afterRefresh(SpringApplication.java:703) [spring-boot-1.5.7.RELEASE.jar:1.5.7.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:304) [spring-boot-1.5.7.RELEASE.jar:1.5.7.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1118) [spring-boot-1.5.7.RELEASE.jar:1.5.7.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1107) [spring-boot-1.5.7.RELEASE.jar:1.5.7.RELEASE]
    at com.kendaya.holidaysplaning.HolidaysPlaningApplication.main(HolidaysPlaningApplication.java:21) [classes/:na]
Caused by: org.springframework.dao.InvalidDataAccessApiUsageException: detached entity passed to persist: com.kendaya.holidaysplaning.entities.WeekDay; nested exception is org.hibernate.PersistentObjectException: detached entity passed to persist: com.kendaya.holidaysplaning.entities.WeekDay
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.convertHibernateAccessException(HibernateJpaDialect.java:299) ~[spring-orm-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:244) ~[spring-orm-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:488) ~[spring-orm-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.dao.support.ChainedPersistenceExceptionTranslator.translateExceptionIfPossible(ChainedPersistenceExceptionTranslator.java:59) ~[spring-tx-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.dao.support.DataAccessUtils.translateIfNecessary(DataAccessUtils.java:213) ~[spring-tx-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:147) ~[spring-tx-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:133) ~[spring-data-jpa-1.11.7.RELEASE.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92) ~[spring-aop-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.data.repository.core.support.SurroundingTransactionDetectorMethodInterceptor.invoke(SurroundingTransactionDetectorMethodInterceptor.java:57) ~[spring-data-commons-1.13.7.RELEASE.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:213) ~[spring-aop-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at com.sun.proxy.$Proxy66.save(Unknown Source) ~[na:na]
    at com.kendaya.holidaysplaning.HolidaysPlaningApplication.lambda$0(HolidaysPlaningApplication.java:39) [classes/:na]
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:732) [spring-boot-1.5.7.RELEASE.jar:1.5.7.RELEASE]
    ... 6 common frames omitted
Caused by: org.hibernate.PersistentObjectException: detached entity passed to persist: com.kendaya.holidaysplaning.entities.WeekDay
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:124) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:765) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:758) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.jpa.event.internal.core.JpaPersistEventListener$1.cascade(JpaPersistEventListener.java:80) ~[hibernate-entitymanager-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:398) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:323) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:162) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:431) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:363) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:326) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:162) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:111) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:456) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:278) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:178) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:109) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.jpa.event.internal.core.JpaPersistEventListener.saveWithGeneratedId(JpaPersistEventListener.java:67) ~[hibernate-entitymanager-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:189) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:132) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:58) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:775) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:748) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:753) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:1146) ~[hibernate-entitymanager-5.0.12.Final.jar:5.0.12.Final]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_91]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_91]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_91]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_91]
    at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:298) ~[spring-orm-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at com.sun.proxy.$Proxy64.persist(Unknown Source) ~[na:na]
    at org.springframework.data.jpa.repository.support.SimpleJpaRepository.save(SimpleJpaRepository.java:508) ~[spring-data-jpa-1.11.7.RELEASE.jar:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_91]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_91]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_91]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_91]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.executeMethodOn(RepositoryFactorySupport.java:504) ~[spring-data-commons-1.13.7.RELEASE.jar:na]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:489) ~[spring-data-commons-1.13.7.RELEASE.jar:na]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:461) ~[spring-data-commons-1.13.7.RELEASE.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:56) ~[spring-data-commons-1.13.7.RELEASE.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99) ~[spring-tx-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:282) ~[spring-tx-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96) ~[spring-tx-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:136) ~[spring-tx-4.3.11.RELEASE.jar:4.3.11.RELEASE]
    ... 17 common frames omitted

Answer 1

As far as I can see, the mapping is correct and everything should work as expected. But the following error message

Caused by: org.hibernate.PersistentObjectException: detached entity passed to persist: com.kendaya.holidaysplaning.entities.WeekDay

is telling you that your day instance is detached. Probably the first repository.save() call is executed in a separate transaction so that after save() call the persistence context is cleared. You have two options to solve the problem:

• Either reread the day record after the first save call before persisting the second department entity, or

   Department d2 = new Department("d2"); WeekDay day1 = repository.find(day.getId()); //!!! pseodocode d2.addWeekDay(day1); repository.save(d2); 

• execute both the repository.save() calls in the same transaction, in which case the day instance is still managed.

Answer 2

Department d1 = new Department("d1");
d1.addWeekDay(day);
repository.save(d1);

Department d2 = new Department("d2");
d2.addWeekDay(sameValuesAsDay);
repository.save(d2);

replace the code with

Department d1 = new Department("d1");
d1.addWeekDay(day);
d1 =repository.save(d1);

Department d2 = new Department("d2");
d2.addWeekDay(sameValuesAsDay);
d2 =repository.save(d2);

Answer 3

I think the accepted answer for this questions, Detached entity passed to persist error , will help you to understand what is the root cause.

In short, hibernate's save method accepts only transient object(ie object created with new operator). When you persist the object using save, that object is no more in the hibernate session (in your case day object) so it throws the error. Try using saveOrUpdate method or as suggested by ujulu, retrieve the day object and then persist.