@Entity(name = "person")
public class Person1 {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@OneToMany(cascade = CascadeType.ALL,orphanRemoval = true)
private List<Phone1> phones = new ArrayList<Phone1>();
public List<Phone1> getPhones() {
return phones;
}
}
@Entity(name = "phone")
public class Phone1 {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private Long id;
@Column(name = "number")
private String number;
public Phone1(String number) {
this.number = number;
}
public Phone1(){};
public Long getId() {
return id;
}
public String getNumber() {
return number;
}
}
@Test
public void test1(){
Session session = sessionFactory.openSession();
session.beginTransaction();
Person1 person = new Person1();
Phone1 phone1 = new Phone1( "123-456-7890" );
Phone1 phone2 = new Phone1( "321-654-0987" );
person.getPhones().add( phone1 );
person.getPhones().add( phone2 );
session.save(person);
session.getTransaction().commit();
session.beginTransaction();
person.getPhones().remove( phone1 );
session.getTransaction().commit();
session.close();
}
以上分别是两张对应的实体类,第3个是我写的测试用例。运行之后的SQL语句是
insert into person values ( )
insert into phone (number) values (?)
insert into phone (number) values (?)
insert into person_phone (person_id, phones_id) values (?, ?)
insert into person_phone (person_id, phones_id) values (?, ?)
delete from person_phone where person_id=?
insert into person_phone (person_id, phones_id) values (?, ?)
delete from phone where id=?
可以看出如果要移除Person的一个号码,会先删除中间表所有与Person有关的数据后再插入。比如person有phone1和phone2两个号码,现在执行操作删除phone1,那么hibernate的做法是会先在中间表删除person与phone的所有关联,然后再插入phone2的数据。
想知道Hibernate为什么会这样执行呢?效率不是太低了吗?