Hibernate在进行one-to-many时的级联设置-cascade

今天在学习Hibernate的one-to-many关联关系时，主键类属性如下：

public class Department implements Serializable {
/**
*
*/
private static final long serialVersionUID = 1L;
private Integer id;
private String name;
private Set<Student> stus;


另一个类的属性如下：
public class Student implements Serializable{
/**
*
*/
private static final long serialVersionUID = 1L;
private Integer id;
private String name;
private Department dept;

通过主键中的Set集合写入数据时，提示：
十月 26, 2015 10:58:40 上午 org.hibernate.engine.jdbc.batch.internal.AbstractBatchImpl release
INFO: HHH000010:<strong> <span style="color:#ff0000;">On release of batch it still contained JDBC statements</span></strong>
Exception in thread "main" java.lang.RuntimeException: <strong><span style="color:#ff0000;">object references an unsaved transient instance - save the transient instance before flushing: com.yel.domain.Student</span></strong>
at com.yel.view.MainTest.main(MainTest.java:45)


原来是主键对应的对应关系映射文件中没有设置级联关系，添加如下设置：
<set name="stus" cascade="save-update">
<key column="dept_id" />
<one-to-many class="Student"/>
</set>设置级联关系的属性为：save-update，这样再进行操作就没有问题啦。