3 つのコード スニペットがあります。
1:
Session session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();
Prepod prepod = (Prepod) session.load(Prepod.class, 1l);
Student student = (Student) session.load(Student.class, 1l);
Hibernate.initialize(prepod.getStudents());
Hibernate.initialize(student.getPrepods());
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();
最初のスニペットが機能し、ログが表示されました。
Hibernate: select prepod0_.id as id1_1_1_, prepod0_.name as name2_1_1_, students1_.prepods_id as prepods1_1_3_, student2_.id as students2_2_3_, student2_.id as id1_0_0_, student2_.age as age2_0_0_, student2_.name as name3_0_0_ from prepod prepod0_ left outer join prepod_Student students1_ on prepod0_.id=students1_.prepods_id left outer join Student student2_ on students1_.students_id=student2_.id where prepod0_.id=?
Hibernate: select student0_.id as id1_0_1_, student0_.age as age2_0_1_, student0_.name as name3_0_1_, prepods1_.students_id as students2_0_3_, prepod2_.id as prepods1_2_3_, prepod2_.id as id1_1_0_, prepod2_.name as name2_1_0_ from Student student0_ left outer join prepod_Student prepods1_ on student0_.id=prepods1_.students_id left outer join prepod prepod2_ on prepods1_.prepods_id=prepod2_.id where student0_.id=?
Hibernate: update Student set age=?, name=? where id=?
2:1から削除
Hibernate.initialize(prepod.getStudents());
Hibernate.initialize(student.getPrepods());
そして、私たちは持っています:
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();
結果：
Exception in thread "main" org.hibernate.LazyInitializationException: could not initialize proxy - no Session
at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:164)
at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:285)
at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)
at logic.Prepod_$$_javassist_1.setStudents(Prepod_$$_javassist_1.java)
at logic.Main.main(Main.java:43)
3:もっと削除
session.close();
と
session = HibernateUtil.getSessionFactory().openSession();
したがって、次のようになります。
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();
このコードの結果：動作し、ログが表示されます：
Hibernate: select prepod0_.id as id1_1_1_, prepod0_.name as name2_1_1_, students1_.prepods_id as prepods1_1_3_, student2_.id as students2_2_3_, student2_.id as id1_0_0_, student2_.age as age2_0_0_, student2_.name as name3_0_0_ from prepod prepod0_ left outer join prepod_Student students1_ on prepod0_.id=students1_.prepods_id left outer join Student student2_ on students1_.students_id=student2_.id where prepod0_.id=?
Hibernate: select student0_.id as id1_0_1_, student0_.age as age2_0_1_, student0_.name as name3_0_1_, prepods1_.students_id as students2_0_3_, prepod2_.id as prepods1_2_3_, prepod2_.id as id1_1_0_, prepod2_.name as name2_1_0_ from Student student0_ left outer join prepod_Student prepods1_ on student0_.id=prepods1_.students_id left outer join prepod prepod2_ on prepods1_.prepods_id=prepod2_.id where student0_.id=?
Hibernate: insert into prepod_Student (prepods_id, students_id) values (?, ?)
この行に特に注意してください。
Hibernate: insert into prepod_Student (prepods_id, students_id) values (?, ?)
この振る舞いは私には理解できません。これらの結果を見た理由を説明してもらえますか?
更新 プリポッド:
@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;
}
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;
}
}
}