hibernate:is not mapped

public void findCustomerAndOrders(){
        Session session = sessionFactory.openSession();
        Transaction tx = null;
        try {
            tx = session.beginTransaction();
            Query query = session.createQuery("from customers as c");
            List list = query.list();
            for(int i = 0 ;i<list.size();i++){
                Customers c = (Customers) list.get(i);
                System.out.println(":"+c.getId());
                System.out.println(":"+c.getName());
                System.out.println(":"+c.getAddress());
                Iterator it = c.getOrderses().iterator();
                while(it.hasNext()){
                    Orders order = (Orders)it.next();
                    System.out.println(order.getOrderNumber()+"  ");
                }
                System.out.println("  ");
            }
            tx.commit();
        } catch(Exception e ){
            if(tx!=null){
                tx.rollback();
            }
            e.printStackTrace();
        } finally {
            session.close();
        }
    }

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="com.yehancheng.bean.Customers" table="customers">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="name" not-null="true" />
        </property>
        <property name="address" type="java.lang.String">
            <column name="address" not-null="true" />
        </property>
        <set name="orderses" inverse="true" cascade="all">
            <key>
                <column name="customerId" not-null="true" />
            </key>
            <one-to-many class="com.yehancheng.bean.Orders" ></one-to-many>
        </set>
    </class>
</hibernate-mapping>