hibernate多表写问题

pojo:
Order   

public class Order implements java.io.Serializable {
private int id;  //订单自动编号
private int orderId; 
private String goodsname;  //商品名
private int goodsid;    //商品ID
private int count;    //购买的数量
private Float price;   //单价
}

Orders：   

public class Orders implements java.io.Serializable{  
private int id;    //编号
private String username;//用户名
private int userid;  //用户编号
private Date submitTime;  //订单提交时间
private Byte ispay;   //是否已付款
private int orderscore;   //订单积分
private java.util.Set ordere=new  java.util.HashSet();
/**   }
 

Orders.hbm.xml:  Orders主键自动递增，one to many Order，
Order对应的Order表中orderid 为外键,references Orders(id);

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.qinge.pojo">
<class name="Orders" table="eOrders">
<id name="id" type="java.lang.Integer">
<column name="Id" /><generator class="increment"/></id>
<property name="username" type="java.lang.String">
<column name="Username" length="20" /></property>
<property name="userid" type="java.lang.Integer">
<column name="Userid" length="" /></property>
<property name="submitTime" type="java.lang.Date">
  <column name="submitTime" length="" /></property>
<property name="ispay" type="java.lang.Byte">
<column name="Ispay" length="1" /></property>
<property name="orderscore" type="java.lang.Integer">
<column name="OrderScore" /></property>
<set name="ordere" inverse="true" lazy="false"><key>
   <column name="Id" precision="10" scale="0" /></key>
                <one-to-many class="com.qinge.pojo.Order" /></set>
</class>
</hibernate-mapping>

像这个两个表插入数据市怎样保持关联？
我有疑惑：向Orders 表写数据时，id未知，向Order 表写数据是怎样确定orderId,以保证数据关联？

cascade="all"