Spring Data Jpa一对多单向映射

/**

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

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生命不息，奋斗不止！

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一对多映射关系

在JPA中，用@OneToMany来标识一对多的关系。实现一对多的单向关联，只需在代表一的实体(Company)中使用@OneToMany映射标注就可以了，代表多的实体不需要使用任何映射标注。

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

Company.java

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;

}

}

Employee.java

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;

}

}

生成的表结构

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

Company.java

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;

}

}

Employee.java

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;

}

}

结构

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