Java JPA 参照完整性约束违反 oneToMany 和批量操作查询
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时间：2020-08-13 00:47:56 来源:igfitidea点击:
JPA Referential integrity constraint violation oneToMany and bulk manipulation query
提问by George
My domain model diagram looks like this:
我的域模型图如下所示：
As you can see I have an oneToMany releation between Student and Attendance and between Attendance and Seminar.
正如你所看到的，我在学生和出勤之间以及出勤和研讨会之间有一个一对多的关系。
Below are the Student and Attendance Classes, as well as my helper class( Initializer).
下面是学生和出勤类，以及我的助手类（初始化器）。
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
考勤班
/**
*
*/
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
初始化类
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 εισ?γουμε τα δεδομ?να διαγρ?φουμε ?τι υπ?ρχει
eraseData();
EntityManager em = DatabaseFactory.createEntityManager();
EntityTransaction tx = em.getTransaction();
tx.begin();
Student s1=new Student("george","antoniou","[email protected]","antoniou","password","998456");
s1.setStudentId(1);
Student s2=new Student("ilias","butsikakis","[email protected]","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 εισ?γουμε τα δεδομ?να διαγρ?φουμε ?τι υπ?ρχει
eraseData();
Student s1=new Student("george","antoniou","[email protected]","antoniou","password","998456");
s1.setStudentId(1);
Student s2=new Student("ilias","butsikakis","[email protected]","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","[email protected]","antoniou","password","998456");
s1.setStudentId(1);
Student s2=new Student("ilias","butsikakis","[email protected]","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.
该项目主要通过 JUnit 测试进行检查，因此在 Initializer Class 中，我们有一个 PrepareData 方法，该方法创建一些用于每次检查的示例数据以及一个删除方法，以确保每次检查都使用相同的数据。
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.
在尝试检查学生和出勤之间的连接之前，一切似乎都正常。我在初始化程序中创建了一个新的出勤对象来测试学生是否可以在研讨会中注册“ok”，并且我收到了很多异常消息。
The one I noticed the most though (as it is shown and in the console) is the
我最注意到的一个（如显示和控制台中所示）是
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]
3781 [main] 错误 org.hibernate.util.JDBCExceptionReporter - 违反参照完整性约束：“FKE7E9BF09F9FEB38B：PUBLIC。”“出勤”“外国钥匙（学生）参考公开。”“学生”“（“学生ID”）SQL 语句：从“学生”中删除 [23003-135]
I checked to make sure the annotations and the cascades are in the right place but with no result...
我检查以确保注释和级联在正确的位置，但没有结果......
I also tried changing the order the items are saved in initilizer class but then other errors appeared
我还尝试更改项目在初始化程序类中保存的顺序，但随后出现了其他错误
**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.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> 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.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##代码##0(ParentRunner.java:41)
> at org.junit.runners.ParentRunner.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
0(ParentRunner.java:41)
at org.junit.runners.ParentRunner.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:
以下是在更改初始化程序类中的项目顺序之前出现的异常列表：
##代码##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.
你能帮我确定为什么会发生这些错误吗？我尝试了我能想到的一切，但收效甚微。任何帮助将不胜感激。
采纳答案by JB Nizet
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.
您试图在删除出勤率之前从数据库中删除所有学生。但是出勤率对学生来说是一个外键。因此，如果数据库允许您删除学生，那么您将拥有一个不连贯的数据库：引用不存在的学生的出勤率。
So you must delete attendances before deleting students.
因此，您必须先删除出勤，然后才能删除学生。
Note that the cascades existing between entities are irrelevant, because insert, update and delete queries completely ignore them.
请注意，实体之间存在的级联是无关紧要的，因为插入、更新和删除查询完全忽略它们。
