属性
CascadeType.REFRESH
:级联刷新,当多个用户同时作操作一个实体,为了用户取到的数据是实时的,在用实体中的数据之前就可以调用一下refresh()方法CascadeType.REMOVE
:级联删除,当调用remove()方法删除Order实体时会先级联删除OrderItem的相关数据CascadeType.MERGE
:级联更新,当调用了Merge()方法,如果Order中的数据改变了会相应的更新OrderItem中的数据CascadeType.PERSIST
:级联保存,当调用了Persist() 方法,会级联保存相应的数据CascadeType.DETACH
:级联脱管/游离操作,如果你要删除一个实体,但是它有外键无法删除,你就需要这个级联权限了。它会撤销所有相关的外键关联。
CascadeType.ALL
:包含以上所有级联属性
级联保存,级联修改,级联删除案例
//学校类
@Table(name = "t_school")
@Entity
@Getter
@Setter
public class School extends BaseEntity {
private String name;
@JsonIgnore
@OneToMany(mappedBy = "school", cascade = {CascadeType.REFRESH, CascadeType.REMOVE, CascadeType.PERSIST}, fetch = FetchType.LAZY)
private List<Student> students = new ArrayList<>();
//手动构造添加学生的方法
public void addStudent(Student stu){
if(!students.contains(stu)){
stu.setSchool(this); //设置学校
this.students.add(stu); //添加
}
}
//重写equals和hashCode方法
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
School school = (School) o;
return Objects.equals(name, school.name) &&
Objects.equals(students, school.students);
}
@Override
public int hashCode() {
return Objects.hash(name, students);
}
}
//学生类
@Table(name = "t_student")
@Entity
@Getter
@Setter
public class Student extends BaseEntity {
private String name;
private String age;
@ManyToOne(cascade = CascadeType.REFRESH,optional = false)
@JoinColumn(name = "SCHOOL_ID")
private School school;
}
//测试类
@RunWith(SpringRunner.class)
@SpringBootTest
public class SchoolDaoTest {
@Autowired
private SchoolDao schoolDao;
@PersistenceContext
private EntityManager em;
@Test
public void testSave() {
School school = new School();
school.setName("学校1");
Student student1 = new Student();
student1.setAge("18");
student1.setName("张三");
Student student2 = new Student();
student2.setAge("18");
student2.setName("李四");
school.addStudent(student1);
school.addStudent(student2);
//经过测试,用save方法也是可以的
schoolDao.saveAndFlush(school); //这个方法dao类需要去继承JpaRepository
}
@Test
public void testDel() {
schoolDao.deleteById(1365157538168864L);
}
@Test
public void testMerge(){
Optional<School> rs = schoolDao.findById(1365164498616352L);
School school = rs.isPresent()? rs.get() : null;
if(school != null){
school.setName("学校2");
List<Student> students = school.getStudents();
if(students != null && students.size() > 0){
for (Student student : students) {
student.setName("改名字");
}
}
school.setStudents(students);
schoolDao.save(school);
}
}
}
经过测试,在保存school的时候会一起把student一起保存,级联保存 删除学校会把级联的student一起删除
级联更新
`cascade`属性加上`CascadeType.MERGE`,注意:不能和懒加载一起使用,正确加载方式:fetch = FetchType.EAGER
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