1.1 many to many relationship

1.1.1 use annotations to complete many to many configuration.
To configure many to many, you only need to configure the intermediate table on one side and use mappedby on the other side to represent foreign key maintenance.
A. Create PO class
    In the Teacher class:
    @Entity
@Table(name="t_teacher")

public class Teacher {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;
    private String name;
    @ManyToMany(targetEntity = Student.class,mappedBy="teacher") / / indicates that the foreign key is maintained by the opposite party
    private Set<Student> students = new HashSet<Student>();

Student Class:
@Entity
@Table(name = "t_student")

public class Student {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;


    private String name;
    @ManyToMany(targetEntity = Teacher.class)
//  Use joinTable to describe the intermediate table, and describe the mapping relationship between foreign key and Student, Teacher in the intermediate table.
//  joinColumn is used to describe the mapping relationship between students and intermediate tables
//  inverseJoinColumn is used to describe the mapping relationship between the Teacher and the intermediate table.
    @JoinTable(name="s_t",joinColumns={@JoinColumn(name="c_student_id")},inverseJoinColumns={@JoinColumn(name="c_teacher_id")})
    private Set<Teacher> students = new HashSet<Teacher>();

//  Test multi-to-multi-level joint saving, save teacher when saving students

    @Test
    public void test4(){
        Session session = hibernateUtils.openSession();
        session.beginTransaction();

//      Create two teachers
        Teacher t1 = new Teacher();
        t1.setName("tommy");

        Teacher t2 = new Teacher();
        t2.setName("hans");

//      Create two students
        Student s1 = new  Student();
        s1.setName("tommy2");

        Student s2 = new  Student();
        s2.setName("hans2");

//      Students relate to teachers
        s1.getTeacher().add(t1);
        s1.getTeacher().add(t2);

        s2.getTeacher().add(t1);
        s2.getTeacher().add(t2);

//      Save students
        session.save(s1);
        session.save(s2);

        session.getTransaction().commit();
        session.close();
    }

Problem: if we establish cascading deletion in many to many.
What happens if we delete tommy?
--All the cascading data is gone.

2. One to one relationship

Take person and ID card number as an example
 1. Create entity class