JPA(4)表表关联关系

    @OrderBy("id")//指的是取出数据的时候，按照哪一个字段来进行排列，我们这里是按照user表的id字段排序,默认是ASC，完整用法：@OrderBy(value= "group_name ASC, name DESC")   
    @OneToMany(targetEntity=Phone.class,mappedBy="user")//mappedBy说的就是上面说的被维护端，多的那一端就是维护端，注意mappedBy="xxx" xxx表示的是在另外一个类中关联这个类的那个属性名，在这个例子中是user

    public Set<Phone> getPhones() {
        return phones;
    }

　　@JoinColumn(name="user_id")//指定外键
    @ManyToOne(targetEntity=User.class)//
    public User getUser() {
        return user;
    }

User.java:   
 @OneToOne(mappedBy="user")//因为需要指定其中一方为被维护段，我们设置user为被维护段
    public FirstLover getFirstLover() {
        return firstLover;
    }
    FirstLover.java:
        //使用OneToOne进行一对一的映射，name表示的是关联关系表的外键,注意的是，这个外键是被维护段的主键，所以是unqie的
    @JoinColumn(unique=true,name="user_id")
    @OneToOne
    public User getUser() {
        return user;
    }

    @JoinColumn(unique=true,name="user_id")
    @OneToOne(fetch=FetchType.LAZY)
    public User getUser() {
        return user;
    }

Student.java:
package com.hotusm.commom.entity;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;



@Entity
public class Student {
    

    private Integer id;
    
    private String name;
    private String sex;
    
    private String school;
    private Set<Teacher> teachers=new HashSet<>();
    
    @GeneratedValue
    @Id
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public String getSchool() {
        return school;
    }
    public void setSchool(String school) {
        this.school = school;
    }
    
    
    @JoinTable(name="teach_stu",//指定中间表的表名，如果没有指定表名，那么默认的名字是：tab1_tab2
            joinColumns={@JoinColumn(name="teacher_id",//指定本类的主键在中间表的外键的字段名称，
            referencedColumnName="ID")},//指定本类的主键是什么，在这个例子中，teach_stu的teacher的id就是本类的主键值
            inverseJoinColumns={@JoinColumn(name="student_id",//和上面是一样的含义，指明另外一个类主键在中间表的名称
                referencedColumnName="ID" //指定另外一个类的主键是什么，这里都是ID
                    )}
            )
    @ManyToMany//加上多对多的标示
    public Set<Teacher> getTeachers() {
        return teachers;
    }
    public void setTeachers(Set<Teacher> teachers) {
        this.teachers = teachers;
    }
    @Override
    public String toString() {
        return this.name;
    }
}
Teacher:
package com.hotusm.commom.entity;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToMany;


@Entity
public class Teacher {
    

    private Integer id;
    
    private String name;
    
    
    private String subjectName;
    
    private Set<Student> students=new HashSet<>();
    
    @GeneratedValue
    @Id
    public Integer getId() {
        return id;
    }
    
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Column(name="SUBJECT_NAME")
    public String getSubjectName() {
        return subjectName;
    }
    public void setSubjectName(String subjectName) {
        this.subjectName = subjectName;
    }
    
    @ManyToMany(mappedBy="teachers")//指定维护的一方，注意这里的名称是另外一个类的属性名： private Set<Teacher> teachers=new HashSet<>();
    public Set<Student> getStudents() {
        return students;
    }
    public void setStudents(Set<Student> students) {
        this.students = students;
    }
    @Override
    public String toString() {
        
        return this.name;
    }
}