Hibernate的关系映射——Ont-To-Many(一对多、多对一)

使用一个例子来表明一对多和多对一的关系（国家、省份和城市之间的关系）

一个国家有多个省份（一对多），多个省份属于一个国家（多对一）

一个省份有多个城市（一对多），多个城市属于一个省份（多对一）

首先，创建三个实体类分别是：Nation（国家），Province（省份），City（城市）

Ont-To-Many：定义多端Set集合，需要实例化HashSet

Many-To-Ont：定义一端对象

Nation（国家）实体类：

[code]public class Nation {

private String nid;
private String nname;

private Set<Province> sp = new HashSet<>();

public Nation() {
super();
// TODO Auto-generated constructor stub
}

public Nation(String nid, String nname, Set<Province> sp) {
super();
this.nid = nid;
this.nname = nname;
this.sp = sp;
}

public String getNid() {
return nid;
}

public void setNid(String nid) {
this.nid = nid;
}

public String getNname() {
return nname;
}

public void setNname(String nname) {
this.nname = nname;
}

public Set<Province> getSp() {
return sp;
}

public void setSp(Set<Province> sp) {
this.sp = sp;
}

@Override
public String toString() {
return "Nation [nid=" + nid + ", nname=" + nname + "]";
}

Province（省份）实体类：

[code]public class Province {

private String pid;
private String pname;
private Nation nation;

private Set<City> sc = new HashSet<>();

public Province() {
super();
// TODO Auto-generated constructor stub
}

public Province(String pid, String pname, Nation nation, Set<City> sc) {
super();
this.pid = pid;
this.pname = pname;
this.nation = nation;
this.sc = sc;
}

public String getPid() {
return pid;
}

public void setPid(String pid) {
this.pid = pid;
}

public String getPname() {
return pname;
}

public void setPname(String pname) {
this.pname = pname;
}

public Nation getNation() {
return nation;
}

public void setNation(Nation nation) {
this.nation = nation;
}

public Set<City> getSc() {
return sc;
}

public void setSc(Set<City> sc) {
this.sc = sc;
}

@Override
public String toString() {
return "Province [pid=" + pid + ", pname=" + pname + "]";
}

City（城市）实体类：

[code]public class City {

private String cid;
private String cname;
private Province province;

public City() {
super();
// TODO Auto-generated constructor stub
}

public City(String cid, String cname, Province province) {
super();
this.cid = cid;
this.cname = cname;
this.province = province;
}

public String getCid() {
return cid;
}

public void setCid(String cid) {
this.cid = cid;
}

public String getCname() {
return cname;
}

public void setCname(String cname) {
this.cname = cname;
}

public Province getProvince() {
return province;
}

public void setProvince(Province province) {
this.province = province;
}

@Override
public String toString() {
return "City [cid=" + cid + ", cname=" + cname + "]";
}

配置三个实体类的映射文件

Nation.hbm.xml

[code]<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2018-9-10 18:29:08 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
<class name="com.zking.entity.Nation" table="NATION">
<id name="nid" type="java.lang.String">
<column name="NID" />
<generator class="guid" />
</id>
<property name="nname" type="java.lang.String">
<column name="NNAME" />
</property>
<set name="sp" table="PROVINCE" cascade="all-delete-orphan"
inverse="true" lazy="false">
<key>
<column name="NID" />
</key>
<one-to-many class="com.zking.entity.Province" />
</set>
</class>
</hibernate-mapping>

Province.hbm.xml

[code]<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2018-9-10 18:29:08 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
<class name="com.zking.entity.Province" table="PROVINCE">
<id name="pid" type="java.lang.String">
<column name="PID" />
<generator class="guid" />
</id>
<property name="pname" type="java.lang.String">
<column name="PNAME" />
</property>
<many-to-one name="nation" class="com.zking.entity.Nation"
fetch="join">
<column name="nid" />
</many-to-one>
<set name="sc" table="CITY" cascade="all-delete-orphan" inverse="true"
lazy="false">
<key>
<column name="PID" />
</key>
<one-to-many class="com.zking.entity.City" />
</set>
</class>
</hibernate-mapping>

City.hbm.xml

[code]<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2018-9-10 18:29:08 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
<class name="com.zking.entity.City" table="CITY">
<id name="cid" type="java.lang.String">
<column name="CID" />
<generator class="guid" />
</id>
<property name="cname" type="java.lang.String">
<column name="CNAME" />
</property>
<many-to-one name="province" class="com.zking.entity.Province"
fetch="join">
<column name="pid" />
</many-to-one>
</class>
</hibernate-mapping>

生成一个唯一的Hibernate映射文件（hibernate.cfg.xml）

[code]<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.password">sasa</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/t204?characterEncoding=UTF-8</property>
<property name="hibernate.connection.username">root</property>

<property name="show_sql">true</property>

<property name="format_sql">true</property>

<mapping resource="com/zking/entity/Nation.hbm.xml" />

<mapping resource="com/zking/entity/Province.hbm.xml" />

<mapping resource="com/zking/entity/City.hbm.xml" />
</session-factory>
</hibernate-
4000
configuration>

大体的创建如下：

最后写一个测试的类（OneToMany.java）级联增加：

[code]public class OneToMany {

@Test
public void add() {
Configuration configuration = new Configuration().configure();
SessionFactory sessionFactory = configuration.buildSessionFactory();
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
// 国家
Nation n1 = new Nation();
n1.setNname("中国");

// 省份
Province p1 = new Province();
p1.setPname("湖南");
Province p2 = new Province();
p2.setPname("广东");

// 城市
City c1 = new City();
c1.setCname("长沙");
City c2 = new City();
c2.setCname("怀化");
City c3 = new City();
c3.setCname("衡阳");
City c4 = new City();
c4.setCname("广州");
City c5 = new City();
c5.setCname("深圳");

// 互设
// 国家里面加省份
n1.getSp().add(p1);
n1.getSp().add(p2);

// 省份里面设置国家
p1.setNation(n1);
p2.setNation(n1);

// 省份里面加城市
p1.getSc().add(c1);
p1.getSc().add(c2);
p1.getSc().add(c3);

p2.getSc().add(c4);
p2.getSc().add(c5);

// 城市里面设置省份
c1.setProvince(p1);
c2.setProvince(p1);
c3.setProvince(p1);

c4.setProvince(p2);
c5.setProvince(p2);

// 保存
session.save(n1);

transaction.commit();
session.close();
sessionFactory.close();
}

}

最后的效果如下：Nation（国家）表

Province（省份）表：

City（城市）表：

三表的级联删除：

[code]public class OneToMany {

@Test
public void delete() {
Configuration configuration = new Configuration().configure();
SessionFactory sessionFactory = configuration.buildSessionFactory();
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Nation n1 = session.get(Nation.class, "472829bf-b4e3-11e8-bcfa-88d7f6a16255");
session.delete(n1);
transaction.commit();
session.close();
sessionFactory.close();
}

}

删除效果则是三表相关联的同一国家的数据都会被删除。