hibernate 外键表如何插入值

Question

3张表 client product trans 
trans中2列对应client product 的主键 
配置如下
1.client
     <set name="transes" inverse="true">
            <key>
                <column name="clientid" not-null="true" />
            </key>
            <one-to-many class="com.hi.Trans" />
        </set>2.product
  <set name="transes" inverse="true">
            <key>
                <column name="productid" not-null="true" />
            </key>
            <one-to-many class="com.hi.Trans" />
        </set>3.trans  <many-to-one name="product" class="com.hi.Product" fetch="select" >
            <column name="productid" not-null="true" />
        </many-to-one>
        <many-to-one name="client" class="com.hi.Client" fetch="select" >
            <column name="clientid" not-null="true" />
        </many-to-one>我想在插入trans插入记录 
写了
Trans trans=new Trans();
Client client=new Client();
Product product=new Product();
client.setClientname("用户姓名");
product.setProductname("产品名称");
trans.setQuantity(new Long(11));
trans.setTdescrition("测试");
trans.setClient(client);
trans.setProduct(product);
TransDAO dao=new TransDAO();
dao.save(trans);提示not-null property references a null or transient value:请问我怎么根据client主键表的中姓名得到它的ID插入到trans
请给具体的插入语句