Analysis of cascading relation operation examples of cascade

cascade Cascading relationship operation example analysis

Today I'd like to share with you cascade Relevant knowledge points of cascading relationship operation example analysis , Detailed content , Clear logic , I believe most people still know too much about this knowledge , So share this article for your reference , I hope you will gain something after reading this article , Now let's take a look .

attribute

• CascadeType.REFRESH： Cascade refresh , When multiple users operate on an entity at the same time , The data obtained for the user is real-time , Before using the data in the entity, you can call refresh() Method

• CascadeType.REMOVE： cascading deletion , When calling remove() Methods to remove Order Entities will be cascaded and deleted first OrderItem Relevant data

• CascadeType.MERGE： update cascade , When calling the Merge() Method , If Order The data in will be updated accordingly OrderItem Data in

• CascadeType.PERSIST： Cascade save , When calling the Persist() Method , The corresponding data will be cascaded and saved

• CascadeType.DETACH： Cascade de tube / Free operation , If you want to delete an entity , But it has foreign keys that cannot be deleted , You need this cascade permission . It will undo all related foreign key associations .

CascadeType.ALL： Contains all of the above cascading properties

Cascade save , Cascade modification , Cascade delete cases

// School @Table(name = "t_school")@[email protected]@Setterpublic 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<>();    // Manually construct the method of adding students     public void addStudent(Student stu){        if(!students.contains(stu)){            stu.setSchool(this);    // Set up school             this.students.add(stu);    // add to         }    }    // rewrite equals and hashCode Method     @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);    }}// Students @Table(name = "t_student")@[email protected]@Setterpublic class Student extends BaseEntity {    private String name;    private String age;    @ManyToOne(cascade = CascadeType.REFRESH,optional = false)    @JoinColumn(name = "SCHOOL_ID")    private School school;}// Test class @RunWith(SpringRunner.class)@SpringBootTestpublic class SchoolDaoTest {    @Autowired    private SchoolDao schoolDao;    @PersistenceContext    private EntityManager em;    @Test    public void testSave() {        School school = new School();        school.setName(" School 1");        Student student1 = new Student();        student1.setAge("18");        student1.setName(" Zhang San ");        Student student2 = new Student();        student2.setAge("18");        student2.setName(" Li Si ");        school.addStudent(student1);        school.addStudent(student2);        // After testing , use save The method is also possible         schoolDao.saveAndFlush(school);        // This method dao Class needs to inherit JpaRepository    }    @Test    public void testDel() {        schoolDao.deleteById(1365157538168864L);    }　　/**　　 *  update cascade 　　 */　　@Test　　public void testMerge(){　　    Optional<School> rs = schoolDao.findById(1365164498616352L);　　    School school = rs.isPresent()? rs.get() : null;　　    if(school != null){　　        school.setName(" School 2");　　        List<Student> students = school.getStudents();　　        if(students != null && students.size() > 0){　　            for (Student student : students) {　　                student.setName(" Change the name ");　　            }　　        }　　        school.setStudents(students);　　        schoolDao.save(school);　　    }　　}}  After testing , In preservation school When we get together student Keep it together , Cascade save   Deleting schools will cascade student Delete cascading updates together `cascade` Attribute plus `CascadeType.MERGE`, Be careful ： Cannot be used with lazy loading , Correct loading method ：fetch = FetchType.EAGER

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