Hibernate中的one-to-many
用一个例子来说明Hibernate中的one-to-many的配置,包含一个Parent(one)和一个Child(many).代码如下：由于使用的是Struts+Hibernate进行试验，所以Parent继承了ActionForm类。
Parent.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd" >
<hibernate-mapping>
<class name="com.ln.hb.Parent" table="parent" >
<id name="pid" column="pid" type="integer">
<generator class="identity" />
</id>
<property name="pname" column="pname" />
<set name="child" lazy="true" inverse="true" cascade="all">
<key column="pid" />
设置子表外键，使得Hibernate可以根据查询结果的主键值与子表外键进行对照，查出所需要的子结果。子表中必须存在这一字段且类型要与主键一致。
<one-to-many class="com.ln.hb.Child"/>
</set>
</class>
</hibernate-mapping>
Parent.java
package com.ln.hb;
import java.util.HashSet;
import org.apache.struts.action.ActionForm;
public class Parent extends ActionForm {
private String pname;
private java.util.Set child = new HashSet();
private int pid;
public Parent() {
}
public int getPid() {
return pid;
}
public void setPid(int pid) {
this.pid = pid;
}
public String getPname() {
return pname;
}
public void setPname(String pname) {
this.pname = pname;
}
public java.util.Set getChild() {
return child;
}
public void setChild(java.util.Set child) {
this.child = child;
}
}
Child.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd" >
<hibernate-mapping>
<class name="com.ln.hb.Child" table="child">
<id name="cid" column="cid" >
<generator class="identity"/>
</id>
<property name="cname" column="cname" />
<many-to-one name="parent" column="pid" />
设置父表外键，使得Hibernate可以根据查询结果的子表外键值与父表的外键值进行对照，查出所需要的父结果。父表中必须存在这一字段且类型要与主键一致。
</class>
</hibernate-mapping>
Child.java
package com.ln.hb;
public class Child {
private String cname;
private String pid;
private Parent parent;
private String cid;
public Child() {
}
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 String getPid() {
return pid;
}
public void setPid(String pid) {
this.pid = pid;
}
public Parent getParent() {
return parent;
}
public void setParent(Parent parent) {
this.parent = parent;
}
}
TestAction.java
package com.ln.struts.action;
import java.util.Iterator;
import java.util.Set;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import net.sf.hibernate.Query;
import net.sf.hibernate.Session;
import net.sf.hibernate.SessionFactory;
import net.sf.hibernate.Transaction;
import net.sf.hibernate.cfg.Configuration;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import com.ln.hb.Child;
import com.ln.hb.Parent;
public class TestAction extends Action {
public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response) throws Exception {
Parent p= (Parent)form;
Child c=new Child();
SessionFactory sf = new Configuration().configure()
.buildSessionFactory();
Session session = sf.openSession();
Transaction tx = session.beginTransaction();
System.out.println("Let's go!");
Query query = session
.createQuery("select p from Parent as p where PID=:pid");
query.setString("pid","1");
for (Iterator it = query.iterate(); it.hasNext();) {
Parent p1=(Parent) it.next();
p.setPname(p1.getPname().toString());
System.out.println(p.getPname());
Set set=p1.getChild();
for(Iterator ic=set.iterator();ic.hasNext();)
{
c=(Child) ic.next();
System.out.println(c.getCname());
}
}
tx.commit();
session.close();
return mapping.findForward("main");
}
}
注意：
1．类中声明的变量的类型要与数据库中类型相一致，所声明的字段在数据库中也要有相应的字段与之对应。
