Hibernate关联关系映射-----单向多对一映射配置

在这里举了一个不太恰当的例子：双亲和孩子。当然举这个例子也有一定的道理，一个孩子至少有两个parent，但是例子只是例子，重点不是例子而是配置方法。下面我们看一下配置的详细步骤：
实体：

package uni.many2one;

public class Child {
private int id;
private String name;

public Child(int id, String name) {
super();
this.id = id;
this.name = name;
}

public Child() {
}

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;
}
}

package uni.many2one;

public class Parent {
private int id;
private String name;
private Child child;

public Parent() {
}

public Parent(int id, String name, Child child) {
super();
this.id = id;
this.name = name;
this.child = child;
}

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;
}

public Child getChild() {
return child;
}

public void setChild(Child child) {
this.child = child;
}

}

hbm配置文件：

<hibernate-mapping>
<class name="uni.many2one.Child">
<id name="id" column="did">
<generator class="native" />
</id>
<property name="name" type="string" column="name"></property>
</class>

</hibernate-mapping>
<hibernate-mapping>
<!-- <class name="org.hibernate.wk.Student" dynamic-insert="true" dynamic-update="true"> -->
<class name="uni.many2one.Parent">
<id name="id" column="did">
<generator class="native" />
</id>
<property name="name" type="string" column="name"></property>

<!-- configure the many to one association -->
<many-to-one name="child" column="child"></many-to-one>
</class>

</hibernate-mapping>

测试文件：

public void testAdd() {
SessionFactory sf = HibernateUtil.getSessionFactory();
Session session = sf.getCurrentSession();
session.beginTransaction();
Child c1 = new Child();
c1.setName("child1");

Parent mother = new Parent();
mother.setName("Mother");
mother.setChild(c1);

Parent father = new Parent();
father.setName("Daddy");
father.setChild(c1);

session.save(c1);
session.save(mother);
session.save(father);
session.beginTransaction().commit();

}

测试结果：

Hibernate: insert into Child (name) values (?)
Hibernate: insert into Parent (name, child) values (?, ?)
Hibernate: insert into Parent (name, child) values (?, ?)

这里我没有贴出来表的结构，因为表hibernate会自动生成的，多以就没有浪费地方。
hibernate关联关系映射的配置中务必要搞清楚谁是主动配置方，谁是被配置的，如果搞不清楚很容易在实体操作的时候出现错误。尤其是在保存实体的时候，很容易出现引用为空的情况。