Java 休眠行为说明:
我有3个代码片段: 1: 2:从1中删除Java 休眠行为说明:,java,hibernate,jpa,orm,Java,Hibernate,Jpa,Orm,我有3个代码片段: 1: 2:从1中删除 Hibernate.initialize(prepod.getStudents()); Hibernate.initialize(student.getPrepods()); 我们有: Session session = HibernateUtil.getSessionFactory().openSession(); session.beginTransaction(); Prepod prep
Hibernate.initialize(prepod.getStudents());
Hibernate.initialize(student.getPrepods());
我们有:
Session session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();
Prepod prepod = (Prepod) session.load(Prepod.class, 1l);
Student student = (Student) session.load(Student.class, 1l);
session.getTransaction().commit();
session.flush();
session.close();
List<Student> students = new ArrayList<Student>();
students.add(student);
List<Prepod> prepods = new ArrayList<Prepod>();
prepods.add(prepod);
prepod.setStudents(students);
student.setPrepods(prepods);
session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();
session.update(student);
session.getTransaction().commit();
session.close();
3:更多删除
session.close();
及
因此,我们:
Session session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();
Prepod prepod = (Prepod) session.load(Prepod.class, 1l);
Student student = (Student) session.load(Student.class, 1l);
session.getTransaction().commit();
session.flush();
List<Student> students = new ArrayList<Student>();
students.add(student);
List<Prepod> prepods = new ArrayList<Prepod>();
prepods.add(prepod);
prepod.setStudents(students);
student.setPrepods(prepods);
session.beginTransaction();
session.update(student);
session.getTransaction().commit();
session.close();
特别注意这一行:
Hibernate: insert into prepod_Student (prepods_id, students_id) values (?, ?)
我不理解这种行为。你能解释我为什么看到这些结果吗
更新
前置词:
@实体
@表(name=“prepd”)
公共类介词{
私人长id;
私有字符串名称;
@纵队
公共字符串getName(){
返回名称;
}
公共void集合名(字符串名){
this.name=名称;
}
List students=new ArrayList();
@ManyToMany(fetch=FetchType.EAGER)
公众学生名单{
留学生;
}
公立学校学生(名单学生){
这个。学生=学生;
}
@身份证
@GeneratedValue(策略=GenerationType.IDENTITY)
@列(name=“id”)
公共长getId(){
返回id;
}
公共无效设置ID(长i){
id=i;
}
学生:
@Entity
@Table(name = "Student")
public class Student {
private Long id;
private String name;
private Long age;
private List<Prepod> prepods = new ArrayList<Prepod>();
@ManyToMany(mappedBy = "students",fetch=FetchType.EAGER)
public List<Prepod> getPrepods() {
return prepods;
}
public void setPrepods(List<Prepod> prepods) {
this.prepods = prepods;
}
public Student() {
name = null;
}
public Student(Student s) {
name = s.getName();
}
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
public Long getId() {
return id;
}
@Column(name = "name")
public String getName() {
return name;
}
@Column(name = "age")
public Long getAge() {
return age;
}
public void setId(Long i) {
id = i;
}
public void setName(String s) {
name = s;
}
public void setAge(Long age) {
this.age = age;
}
}
}
@实体
@表(name=“Student”)
公立班学生{
私人长id;
私有字符串名称;
私人长寿;
private List preposd=new ArrayList();
@ManyToMany(mappedBy=“students”,fetch=FetchType.EAGER)
公共列表getPrepDS(){
返回介词;
}
公共void setprepDS(列表prepDS){
this.preposds=preposds;
}
公立学生(){
name=null;
}
公立学生{
name=s.getName();
}
@身份证
@GeneratedValue(策略=GenerationType.IDENTITY)
@列(name=“id”)
公共长getId(){
返回id;
}
@列(name=“name”)
公共字符串getName(){
返回名称;
}
@列(name=“age”)
公共长假{
回归年龄;
}
公共无效设置ID(长i){
id=i;
}
公共void集合名(字符串s){
name=s;
}
公共空间设置(长时间){
这个。年龄=年龄;
}
}
}
Hibernate使用其自定义的代理
,HibernateProxy
包装延迟加载的集合和对象。每一个都有一个LazyInitializer
实例来初始化对象(因为它还没有完全加载)
这些LazyInitializer
实例扩展了AbstractLazyInitializer
方法AbstractLazyInitializer.initialize()
具有以下内容(我们感兴趣)
在第一个片段中,调用
Hibernate.initialize(prepod.getStudents());
Hibernate.initialize(student.getPrepods());
在关闭初始化Hibernate代理(即prepod
和student
对象)的会话之前。因此,它们的initialized
标志被设置为true,并且将来与对象的所有交互都跳过if
块
在第二个代码段中,您不会初始化代理
并关闭会话
。当你试着打电话的时候
prepod.setStudents(students);
它将失败,因为initialized
为false,而会话
为null
else if ( session == null ) {
throw new LazyInitializationException( "could not initialize proxy - no Session" );
}
在第三个代码段中,您没有关闭会话
,因此
prepod.setStudents(students);
将不间断地执行初始化 在所有示例中,我都使用了渴望初始化。我认为它加载了关系集合。@user2674303继续并发布您的实体映射。@User您比我更适合检查,但Hibernate仍然会代理您的类,即使您已经加载了关系集合。@user2674303使用调试器。您会注意到prepd
引用的类类型实际上是prepd\u$$\ uJavassist\u1
类型的代理。
@Entity
@Table(name = "prepod")
public class Prepod {
private Long id;
private String name;
@Column
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
List<Student> students = new ArrayList<Student>();
@ManyToMany(fetch=FetchType.EAGER)
public List<Student> getStudents() {
return students;
}
public void setStudents(List<Student> students) {
this.students = students;
}
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
public Long getId() {
return id;
}
public void setId(Long i) {
id = i;
}
@Entity
@Table(name = "Student")
public class Student {
private Long id;
private String name;
private Long age;
private List<Prepod> prepods = new ArrayList<Prepod>();
@ManyToMany(mappedBy = "students",fetch=FetchType.EAGER)
public List<Prepod> getPrepods() {
return prepods;
}
public void setPrepods(List<Prepod> prepods) {
this.prepods = prepods;
}
public Student() {
name = null;
}
public Student(Student s) {
name = s.getName();
}
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
public Long getId() {
return id;
}
@Column(name = "name")
public String getName() {
return name;
}
@Column(name = "age")
public Long getAge() {
return age;
}
public void setId(Long i) {
id = i;
}
public void setName(String s) {
name = s;
}
public void setAge(Long age) {
this.age = age;
}
}
}
public final void initialize() throws HibernateException {
if ( !initialized ) {
if ( specjLazyLoad ) {
specialSpecjInitialization();
}
else if ( session == null ) {
throw new LazyInitializationException( "could not initialize proxy - no Session" );
}
...
}
}
Hibernate.initialize(prepod.getStudents());
Hibernate.initialize(student.getPrepods());
prepod.setStudents(students);
else if ( session == null ) {
throw new LazyInitializationException( "could not initialize proxy - no Session" );
}
prepod.setStudents(students);