/**
- @author StormMaybin
- @date 2017-01-17
*/
生命不息，奋斗不止！
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)
