/**
- @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@GeneratedValueprivate 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@GeneratedValueprivate 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@GeneratedValueprivate 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@GeneratedValueprivate 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)
