Spring Data Jpa一对多单向映射

/**

• @author StormMaybin
• @date 2017-01-17
  
  */

---

---

一对多映射关系

有两种方式实现一对多的单向关联。一种是在只使用@OneToMany来标识，这种方式是通过一张第三方表来保存关系。还有一种是使用@OneToMany和@JoinColumn来标注，这种方式是在多的一方(Employee)的表中增加一个外键列来保存关系。

OneToMany

package com.stormma.model;

import java.util.List;

import javax.persistence.CascadeType;


import javax.persistence.Entity;


import javax.persistence.GeneratedValue;


import javax.persistence.Id;


import javax.persistence.OneToMany;


import javax.persistence.Table;

/**
Created by mayongbin01 on 2017/1/17.


*/


@Entity


@Table(name = "company")


public class Company {

//唯一标识公司


@Id


@GeneratedValue


private int id;

//公司名字


private String name;

@OneToMany(cascade = {CascadeType.ALL})


private List<Employee> employees;

public int getId() {


return id;


}

public void setId(int id) {


this.id = id;


}

public String getName() {


return name;


}

public void setName(String name) {


this.name = name;


}


}

package com.stormma.model;

import javax.persistence.Entity;


import javax.persistence.GeneratedValue;


import javax.persistence.Id;


import javax.persistence.Table;

/**
Created by mayongbin01 on 2017/1/17.


*/


@Entity


@Table(name = "employee")


public class Employee {

//唯一标识雇员


@Id


@GeneratedValue


private int id;

private String name;

public int getId() {


return id;


}

public void setId(int id) {


this.id = id;


}

public String getName() {


return name;


}

public void setName(String name) {


this.name = name;


}


}

CREATE TABLE `employee` (

  `id` int(11) NOT NULL AUTO_INCREMENT,

  `name` varchar(255) DEFAULT NULL,

  PRIMARY KEY (`id`)

) ENGINE=InnoDB DEFAULT CHARSET=latin1;

DROP TABLE IF EXISTS company;


CREATE TABLE company (


id int(11) NOT NULL AUTO_INCREMENT,


name varchar(255) DEFAULT NULL,


PRIMARY KEY (id)


) ENGINE=InnoDB DEFAULT CHARSET=latin1;

DROP TABLE IF EXISTS company_employees;


CREATE TABLE company_employees (


company_id int(11) NOT NULL,


employees_id int(11) NOT NULL,


UNIQUE KEY UK_lg2r1rg13q18sa62l1y7un4or (employees_id),


KEY FKd66w6jx84tydyd8sf9mpqh5je (company_id),


CONSTRAINT FKd66w6jx84tydyd8sf9mpqh5je FOREIGN KEY (company_id) REFERENCES company (id),


CONSTRAINT FKnntnqhhla66c4h9ddbnlvqk2x FOREIGN KEY (employees_id) REFERENCES employee (id)


) ENGINE=InnoDB DEFAULT CHARSET=latin1;

OneToMany+JoinColumn

package com.stormma.model;

import java.util.List;

import javax.persistence.CascadeType;


import javax.persistence.Entity;


import javax.persistence.GeneratedValue;


import javax.persistence.Id;


import javax.persistence.JoinColumn;


import javax.persistence.OneToMany;


import javax.persistence.Table;

/**
Created by mayongbin01 on 2017/1/17.


*/


@Entity


@Table(name = "company")


public class Company {

//唯一标识公司


@Id


@GeneratedValue


private int id;

//公司名字


private String name;

@OneToMany(cascade = CascadeType.ALL)


@JoinColumn(name = "company_id")


private List<Employee> employees;

public int getId() {


return id;


}

public void setId(int id) {


this.id = id;


}

public String getName() {


return name;


}

public void setName(String name) {


this.name = name;


}


}

package com.stormma.model;

import javax.persistence.Entity;


import javax.persistence.GeneratedValue;


import javax.persistence.Id;


import javax.persistence.Table;

/**
Created by mayongbin01 on 2017/1/17.


*/


@Entity


@Table(name = "employee")


public class Employee {

//唯一标识雇员


@Id


@GeneratedValue


private int id;

private String name;

public int getId() {


return id;


}

public void setId(int id) {


this.id = id;


}

public String getName() {


return name;


}

public void setName(String name) {


this.name = name;


}


}

Hibernate: create table company (id integer not null auto_increment, name varchar(255), primary key (id))

Hibernate: create table employee (id integer not null auto_increment, name varchar(255), company_id integer, primary key (id))

Hibernate: alter table employee add constraint FK5v50ed2bjh60n1gc7ifuxmgf4 foreign key (company_id) references company (id)

原文地址：https://www.jianshu.com/p/0a2163273b3e