Hibernate中的一对多、多对一、多对多(MySQL)

Posted on In , , Waline:

一对多 / 多对一：

Department.java

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package com.laisc.hibernatetest002.entity;

import jakarta.persistence.*;

import java.util.ArrayList;
import java.util.List;

@Entity
public class Department {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    // 一对多
    @OneToMany(mappedBy = "department", cascade = CascadeType.ALL)
    private List<Employee> employees = new ArrayList<>();
}

Employee.java

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package com.laisc.hibernatetest002.entity;

import jakarta.persistence.*;

@Entity
public class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    // 多对一
    @ManyToOne
    @JoinColumn(name = "department_id", referencedColumnName = "id") //字段名为id
    private Department department;
}

多对多

Student.java

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package com.laisc.hibernatetest002.entity.ManyToMany;

import jakarta.persistence.*;

import java.util.ArrayList;
import java.util.List;

@Entity
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    @ManyToMany
    @JoinTable(
            name = "student_course",
            joinColumns = @JoinColumn(name = "student_id",               // 中间表字段名
                    referencedColumnName = "id" // 对应 Student 表的 id 列
            ),
            inverseJoinColumns = @JoinColumn(name = "course_id",                // 中间表字段名
                    referencedColumnName = "id"  // 对应 Course 表的 id 列
            )
    )
    private List<Course> courses = new ArrayList<>();
}

Course.java

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package com.laisc.hibernatetest002.entity.ManyToMany;

import jakarta.persistence.*;

import java.util.ArrayList;
import java.util.List;

@Entity
public class Course {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String title;

    @ManyToMany(mappedBy = "courses")
    private List<Student> students = new ArrayList<>();
}