/**
- @author StormMaybin
- @date 2017-01-17
*/
生命不息懂算，奮斗不止计技！
一對(duì)多映射關(guān)系
在JPA中山橄，用@OneToMany來(lái)標(biāo)識(shí)一對(duì)多的關(guān)系。實(shí)現(xiàn)一對(duì)多的單向關(guān)聯(lián)涣澡，只需在代表一的實(shí)體(Company)中使用@OneToMany映射標(biāo)注就可以了丧诺，代表多的實(shí)體不需要使用任何映射標(biāo)注驳阎。
有兩種方式實(shí)現(xiàn)一對(duì)多的單向關(guān)聯(lián)。一種是在只使用@OneToMany來(lái)標(biāo)識(shí)蜘腌，這種方式是通過(guò)一張第三方表來(lái)保存關(guān)系饵隙。還有一種是使用@OneToMany和@JoinColumn來(lái)標(biāo)注金矛，這種方式是在多的一方(Employee)的表中增加一個(gè)外鍵列來(lái)保存關(guān)系勺届。
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 {
//唯一標(biāo)識(shí)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 {
//唯一標(biāo)識(shí)雇員
@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;
}
}
生成的表結(jié)構(gòu)
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 {
//唯一標(biāo)識(shí)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 {
//唯一標(biāo)識(shí)雇員
@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;
}
}
結(jié)構(gòu)
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)
