My domain model diagram looks like this:
As you can see I have an oneToMany releation between Student and Attendance and between Attendance and Seminar.
Below are the Student and Attendance Classes, as well as my helper class( Initializer).
package com.seminars.domain;
import java.util.Calendar;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import org.hibernate.annotations.GenericGenerator;
import com.seminars.util.SimpleCalendar;
@Entity
@Table(name="Student")
public class Student {
/*start all class fields*/
@Id
//@GenericGenerator(name="kaugen" , strategy="increment")
//@GeneratedValue(generator="kaugen")
@Column(name="studentId")
//@GeneratedValue(strategy=GenerationType.AUTO)
private int studentId;
@Column(name="firstname", length=50, nullable = false)
private String firstname;
@Column(name="lastname", length=50, nullable = false)
private String lastname;
@Column(name="email", length=50, nullable = false)
private String email;
@Column(name="username", length=50, nullable = false)
private String username;
@Column(name="password", length=50, nullable = false)
private String password;
@Column(name="idCard", length=50, nullable = false)
private String idCard;
/* end fields*/
@OneToMany(mappedBy = "student",cascade=CascadeType.ALL)
private Set<Attendance> attendance = new HashSet<Attendance>() ;
/**
* default constructor
*/
public Student(){
}
/**
* Secondary Constructor to automatically create a Student
* @param firstname
* @param lastname
* @param email
* @param username
* @param password
* @param idcard
*/
public Student(String firstname,String lastname,String email, String username,String password, String idcard){
this.setFirstname(firstname);
this.setLastname(lastname);
this.setEmail(email);
this.setIdCard(idcard);
this.setPassword(password);
this.setUsername(username);
}
public int getStudentId() {
return studentId;
}
public void setStudentId(int studentId) {
this.studentId = studentId;
}
public String getFirstname() {
return firstname;
}
public void setFirstname(String firstname) {
this.firstname = firstname;
}
public String getLastname() {
return lastname;
}
public void setLastname(String lastname) {
this.lastname = lastname;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getIdCard() {
return idCard;
}
public void setIdCard(String idCard) {
this.idCard = idCard;
}
/*Methods for connecting Student<------->Attendance*/
/**
* @return a new hashset contain
* <p>all attendances of the student
*/
public HashSet<Attendance> getAttendance(){
return new HashSet<Attendance>(attendance);
}
/**
* @param attendance
* @param seminar
*/
public void addAttendance(Attendance attendance, Seminar seminar){
if(attendance!=null & seminar!=null){
attendance.setStudent(this);
attendance.setSeminar(seminar);
attendance.setRegisterDate((new SimpleCalendar(Calendar.getInstance()))); /* xreiazomaste na orizete I timi apo to sistima automata*/
}
}
/**
* @param attendance to remove from HashSet
*/
public void removeAttendance(Attendance attendance){
attendance.setStudent(null);
}
/**
* @return Attendance HashSet
*/
public Set<Attendance> findAttendance(){
return attendance;
}
/* (non-Javadoc)
* @see java.lang.Object#equals(java.lang.Object)
*/
public boolean equals(Object other) {
if ( other == null) {
return false;
}
if (this == other) {
return true;
}
if (! (other instanceof Student)) {
return false;
}
Student theStudent = (Student) other;
//Integer a=getStudentId();
//Integer b=theStudent.getStudentId();
if(!(getIdCard()==null) ? theStudent.getIdCard()==null : getIdCard().equals(theStudent.getIdCard())){
return false;
}
return true;
}
/* (non-Javadoc)
* @see java.lang.Object#hashCode()
*/
public int hashCode() {
return idCard == null ? 0 : idCard.hashCode();
}
}
Attendance Class
/**
*
*/
package com.seminars.domain;
import java.util.Calendar;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import org.junit.Assert;
import org.junit.Test;
import com.seminars.util.SimpleCalendar;
/**
* @author Ilias
*
*/
@Entity
@Table(name = "Attendance")
public class Attendance {
public Attendance() {
this.registerDate=new SimpleCalendar(Calendar.getInstance());
}
@Id
@Column(name="attendanceId")
@GeneratedValue(strategy=GenerationType.AUTO)
private int attendanceId;
@Column(name = "registerDate", length = 200, nullable = false)
//@Temporal(TemporalType.DATE)
@org.hibernate.annotations.Type(
type="com.seminars.persistence.SimpleCalendarCustomType")
private SimpleCalendar registerDate;
@Column(name = "success")
private boolean success;
@ManyToOne
@JoinColumn(name="studentId", nullable = false)
private Student student;
@OneToMany(mappedBy = "attendance",cascade=CascadeType.ALL)
private Set<Absence> absence = new HashSet<Absence>() ;
@ManyToOne
@JoinColumn(name="seminarId", nullable = false)
private Seminar seminar;
@OneToMany(mappedBy = "attendance",cascade=CascadeType.ALL)
private Set<Payment> payment = new HashSet<Payment>() ;/*<<<*/
public SimpleCalendar getRegisterDate() {
return registerDate;
}
public void setRegisterDate(SimpleCalendar registerDate) {
this.registerDate = registerDate;
}
public boolean isSuccess() {
return success;
}
public void setSuccess(boolean success) {
this.success = success;
}
/**
* @return the student
*/
public Student getStudent() {
return student;
}
/**
* @param student the student to set
*/
public void setStudent(Student student) {
//this.student = student.findAttendance().add(this);
if (this.student != null) {
this.student.findAttendance().remove(this);
}
this.student = student;
if (this.student != null) {
this.student.findAttendance().add(this);
}
}
/**
* @return the seminar
*/
public Seminar getSeminar() {
return seminar;
}
/**
* @param seminar the seminar to set
*/
public void setSeminar(Seminar seminar) {
//this.student = student.findAttendance().add(this);
if (this.seminar != null) {
this.seminar.findAttendance().remove(this);
}
this.seminar = seminar;
if (this.seminar != null) {
this.seminar.findAttendance().add(this);
}
}
public HashSet<Absence> getAbsence(){
return new HashSet<Absence>(absence);
}
public void addAbsence(Absence absence, SimpleCalendar date){
if(absence!=null && date!=null){
absence.setAttendance(this);
/*stelnoume tin imerominia pou kataxorei I gramamteia oti elipe o foititis*/
absence.setDate(date);
}
}
/**
* @return Absence HashSet
*/
public Set<Absence> findAbsence(){
return absence;
}
/**
* @return HashSet<Payment>
*/
public HashSet<Payment> getPayment(){
return new HashSet<Payment>(payment);
}
public void addPayment(Payment payment, SimpleCalendar date){
if(payment!=null && date!=null){
payment.setAttendance(this);
/*stelnoume tin imerominia pou kataxorei I gramamteia oti elipe o foititis*/
//absence.setDate(date);
}
}
/**
* @return Payment HashSet
*/
public Set<Payment> findPayment(){
return payment;
}
/* (non-Javadoc)
* @see java.lang.Object#equals(java.lang.Object)
*/
@Override
public boolean equals(Object other) {
if ( other == null) {
return false;
}
if (this == other) {
return true;
}
if (! (other instanceof Attendance)) {
return false;
}
Attendance theAttendance = (Attendance) other;
//Integer a=getStudentId();
//Integer b=theStudent.getStudentId();
if(!(getStudent()==null) ? theAttendance.getStudent()==null : getStudent().equals(theAttendance.getStudent())){
return false;
}
if(!(getSeminar()==null) ? theAttendance.getSeminar()==null : getSeminar().equals(theAttendance.getSeminar())){
return false;
}
return true;
}
/* (non-Javadoc)
* @see java.lang.Object#hashCode()
*/
public int hashCode() {
if(student==null && seminar==null){
return 0;
}
else {
int result=0;
if(student!=null)
result+= 13*getStudent().hashCode()/*+getSeminar().hashCode()*/;
if(seminar!=null)
result+= 13*getSeminar().hashCode();
return result;
}
/*int result = 0;
result = getStudent() == null ? result : 13 * result + getStudent().hashCode();
result = getSeminar() == null ? result : 13 * result + getSeminar().hashCode();
return result; */
}
}
Initializer Class
package com.seminars.persistence;
import java.util.Calendar;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;
import javax.persistence.Query;
import com.seminars.domain.Attendance;
import com.seminars.domain.Seminar;
import com.seminars.domain.Student;
import com.seminars.util.SimpleCalendar;
public class Initializer {
/* EntityManager em = DatabaseFactory.createEntityManager();
EntityTransaction tx = em.getTransaction();*/
//delete all data from database
public void eraseData() {
EntityManager em = DatabaseFactory.getCurrentEntityManager();
EntityTransaction tx = em.getTransaction();
tx.begin();
Query query = em.createNativeQuery("delete from \"Student\"");
query.executeUpdate();
query = em.createNativeQuery("delete from \"Absence\"");
query.executeUpdate();
query = em.createNativeQuery("delete from \"Attendance\"");
query.executeUpdate();
query = em.createNativeQuery("delete from \"Payment\"");
query.executeUpdate();
query = em.createNativeQuery("delete from \"Seminar\"");
query.executeUpdate();
query = em.createNativeQuery("delete from \"Program\"");
query.executeUpdate();
tx.commit();
em.close();
}
public void prepareData() {
// πριν εισάγουμε τα δεδομένα διαγράφουμε ότι υπάρχει
eraseData();
EntityManager em = DatabaseFactory.createEntityManager();
EntityTransaction tx = em.getTransaction();
tx.begin();
Student s1=new Student("george","antoniou","antoniougeo@hotmail.com","antoniou","password","998456");
s1.setStudentId(1);
Student s2=new Student("ilias","butsikakis","ili@hotmail.com","ilias","butsi","98756423");
s2.setStudentId(2);
Seminar sem1=new Seminar(1, "Java", 5,500, 2, new SimpleCalendar(2013,1,5), new SimpleCalendar(2013,2,5),"100");
sem1.setSeminarId(1);
Attendance att=new Attendance();
att.setRegisterDate(new SimpleCalendar(Calendar.getInstance()));
//s1.addAttendance(att, sem1);
//s1=em.merge(s1);
//s2=em.merge(s2);
//sem1=em.merge(sem1);
//em.persist(att);
em.persist(s1);
em.persist(s2);
em.persist(sem1);
s1.addAttendance(att, sem1);
em.persist(att);
s1=em.merge(s1);
em.persist(s1);
tx.commit();
em.close();
}
/*public void prepareData1() {
// πριν εισάγουμε τα δεδομένα διαγράφουμε ότι υπάρχει
eraseData();
Student s1=new Student("george","antoniou","antoniougeo@hotmail.com","antoniou","password","998456");
s1.setStudentId(1);
Student s2=new Student("ilias","butsikakis","ili@hotmail.com","ilias","butsi","98756423");
s2.setStudentId(2);
Seminar sem1=new Seminar(1, "Java", 5,500, 2, new SimpleCalendar(2013,1,5), new SimpleCalendar(2013,2,5),"100");
//EntityManager em = DatabaseFactory.createEntityManager();
EntityManager em = DatabaseFactory.createEntityManager();
EntityTransaction tx = em.getTransaction();
tx.begin();
em.persist(s1);
em.persist(s2);
tx.commit();
em.close();
/*NOTE ALWAYS REMEMBER:
* 1)Open entity Manager,
* 2)Open Transaction
* 3)Create Items
* else You will need to use merge or you will get a detached exception!!!
* */
//s1=em.merge(s1);
/* Student s1=new Student("george","antoniou","antoniougeo@hotmail.com","antoniou","password","998456");
s1.setStudentId(1);
Student s2=new Student("ilias","butsikakis","ili@hotmail.com","ilias","butsi","98756423");
s2.setStudentId(2);
Seminar sem1=new Seminar(1, "Java", 5,500, 2, new SimpleCalendar(2013,1,5), new SimpleCalendar(2013,2,5),"100");
s1=em.merge(s1);
s2=em.merge(s2);
sem1=em.merge(sem1);
em.persist(s1);
em.persist(s2);
em.persist(sem1);
tx.commit();
em.close();*/
/*EntityManagerFactory emf = Persistence.createEntityManagerFactory("library");
EntityManager em = emf.createEntityManager();*/
//}
}
The project is mostly checked through JUnit Tests, so in Initializer Class we have a PrepareData method which creates some sample data to use in each check as well a delete method to make sure each check is done with the same data.
Before trying to check the connection between Student and Attendance everything seemed to work ok. I went and created a new Attendance Object in initializer to test if the Student can enroll "ok" in a seminar and I got a lot of Exception messages.
The one I noticed the most though (as it is shown and in the console) is the
3781 [main] ERROR org.hibernate.util.JDBCExceptionReporter - Referential integrity constraint violation: "FKE7E9BF09F9FEB38B: PUBLIC.""Attendance"" FOREIGN KEY(STUDENT) REFERENCES PUBLIC.""Student""(""studentId"")"; SQL statement: delete from "Student" [23003-135]
I checked to make sure the annotations and the cascades are in the right place but with no result...
I also tried changing the order the items are saved in initilizer class but then other errors appeared
**javax.persistence.PersistenceException: org.hibernate.PropertyValueException: not-null property references a null or transient value: com.seminars.domain.Attendance.seminar**
at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1235)
at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1168)
at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1174)
at org.hibernate.ejb.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:674)
at com.seminars.persistence.Initializer.prepareData(Initializer.java:73)
at com.seminars.services.ManageStudentServiceTest.setup(ManageStudentServiceTest.java:60)
at com.seminars.services.ManageStudentServiceTest.testManageStudentService(ManageStudentServiceTest.java:97)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:44)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:180)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:41)
at org.junit.runners.ParentRunner$1.evaluate(ParentRunner.java:173)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
at org.junit.runners.ParentRunner.run(ParentRunner.java:220)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: org.hibernate.PropertyValueException: not-null property references a null or transient value: com.seminars.domain.Attendance.seminar
at org.hibernate.engine.Nullability.checkNullability(Nullability.java:101)
at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:313)
at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:204)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:130)
at org.hibernate.ejb.event.EJB3PersistEventListener.saveWithGeneratedId(EJB3PersistEventListener.java:69)
at org.hibernate.event.def.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:179)
at org.hibernate.event.def.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:135)
at org.hibernate.event.def.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:61)
at org.hibernate.impl.SessionImpl.firePersist(SessionImpl.java:800)
at org.hibernate.impl.SessionImpl.persist(SessionImpl.java:774)
at org.hibernate.impl.SessionImpl.persist(SessionImpl.java:778)
at org.hibernate.ejb.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:668)
... 27 more
Below is the Exception list that came up before changing the order of the items in the initializer class:
> javax.persistence.PersistenceException:
> org.hibernate.exception.ConstraintViolationException: could not
> execute native bulk manipulation query at
> org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1235)
> at
> org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1168)
> at
> org.hibernate.ejb.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:1245)
> at
> org.hibernate.ejb.AbstractQueryImpl.executeUpdate(AbstractQueryImpl.java:108)
> at
> com.seminars.persistence.Initializer.eraseData(Initializer.java:37)
> at
> com.seminars.services.ManageStudentServiceTest.empty(ManageStudentServiceTest.java:64)
> at
> com.seminars.services.ManageStudentServiceTest.testManageStudentService(ManageStudentServiceTest.java:99)
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at
> sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at
> java.lang.reflect.Method.invoke(Unknown Source) at
> org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
> at
> org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
> at
> org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
> at
> org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
> at
> org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
> at
> org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
> at
> org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
> at
> org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:44)
> at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:180)
> at org.junit.runners.ParentRunner.access$000(ParentRunner.java:41)
> at org.junit.runners.ParentRunner$1.evaluate(ParentRunner.java:173)
> at
> org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
> at
> org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
> at org.junit.runners.ParentRunner.run(ParentRunner.java:220) at
> org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
> at
> org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
> at
> org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
> at
> org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
> at
> org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
> at
> org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
> Caused by: org.hibernate.exception.ConstraintViolationException: could
> not execute native bulk manipulation query at
> org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:96)
> at
> org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
> at
> org.hibernate.engine.query.NativeSQLQueryPlan.performExecuteUpdate(NativeSQLQueryPlan.java:219)
> at
> org.hibernate.impl.SessionImpl.executeNativeUpdate(SessionImpl.java:1300)
> at
> org.hibernate.impl.SQLQueryImpl.executeUpdate(SQLQueryImpl.java:365)
> at
> org.hibernate.ejb.QueryImpl.internalExecuteUpdate(QueryImpl.java:183)
> at
> org.hibernate.ejb.AbstractQueryImpl.executeUpdate(AbstractQueryImpl.java:99)
> ... 27 more Caused by: org.h2.jdbc.JdbcSQLException: Referential
> integrity constraint violation: "FKE7E9BF09F9FEB38B:
> PUBLIC.""Attendance"" FOREIGN KEY(STUDENT) REFERENCES
> PUBLIC.""Student""(""studentId"")"; SQL statement: delete from
> "Student" [23003-135] at
> org.h2.message.DbException.getJdbcSQLException(DbException.java:327)
> at org.h2.message.DbException.get(DbException.java:167) at
> org.h2.message.DbException.get(DbException.java:144) at
> org.h2.constraint.ConstraintReferential.checkRow(ConstraintReferential.java:378)
> at
> org.h2.constraint.ConstraintReferential.checkRowRefTable(ConstraintReferential.java:395)
> at
> org.h2.constraint.ConstraintReferential.checkRow(ConstraintReferential.java:275)
> at org.h2.table.Table.fireConstraints(Table.java:788) at
> org.h2.table.Table.fireAfterRow(Table.java:805) at
> org.h2.command.dml.Delete.update(Delete.java:79) at
> org.h2.command.CommandContainer.update(CommandContainer.java:70) at
> org.h2.command.Command.executeUpdate(Command.java:199) at
> org.h2.jdbc.JdbcPreparedStatement.executeUpdateInternal(JdbcPreparedStatement.java:141)
> at
> org.h2.jdbc.JdbcPreparedStatement.executeUpdate(JdbcPreparedStatement.java:127)
> at
> org.hibernate.engine.query.NativeSQLQueryPlan.performExecuteUpdate(NativeSQLQueryPlan.java:210)
> ... 31 more
Can you please help me determine why these errors Happen? I tried everything I could think but with little success. Any help would be greatly appreciated.
You're trying to delete all the students from the database before deleting the attendances. But attendance has a foreign key to student. So, if the database let you delete the students, you would have an incoherent database: attendances referencing students that don't exist.
So you must delete attendances before deleting students.
Note that the cascades existing between entities are irrelevant, because insert, update and delete queries completely ignore them.
来源：https://stackoverflow.com/questions/20276817/jpa-referential-integrity-constraint-violation-onetomany-and-bulk-manipulation-q