Hibernate一对多关联映射的配置及其级联删除问题

package com.exam.entity;
import java.util.Set;
public class QuestionType {
	private String typeName;
	private char typeUniqueness;
	private Set quesion;
	public String getTypeName() {
		return typeName;
	}
	public void setTypeName(String typeName) {
		this.typeName = typeName;
	}
	public char getTypeUniqueness() {
		return typeUniqueness;
	}
	public void setTypeUniqueness(char typeUniqueness) {
		this.typeUniqueness = typeUniqueness;
	}
	public Set getQuesion() {
		return quesion;
	}
	public void setQuesion(Set quesion) {
		this.quesion = quesion;
	}
}

<hibernate-mapping package="com.exam.entity">
	<class name="QuestionType" table="exam_question_type">
		<id name="typeName" column="type_name"></id>
		<property name="typeUniqueness"  column="type_uniqueness"/>
		<set name="quesion" inverse="true" cascade="delete">
			<key column="question_type_name"/>
			<one-to-many class="Question"/>
		</set>
	</class>
</hibernate-mapping>

package com.exam.entity;
import java.util.Date;
public class Question {
	private int questionNo;
	private QuestionType questionType;
	private String questionsTitle;
	public int getQuestionNo() {
		return questionNo;
	}
	public void setQuestionNo(int questionNo) {
		this.questionNo = questionNo;
	}
	public QuestionType getQuestionType() {
		return questionType;
	}
	public void setQuestionType(QuestionType questionType) {
		this.questionType = questionType;
	}
	public String getQuestionsTitle() {
		return questionsTitle;
	}
	public void setQuestionsTitle(String questionsTitle) {
		this.questionsTitle = questionsTitle;
	}
}

<hibernate-mapping package="com.exam.entity">
	<class name="Question" table="exam_question">
		<id name="questionNo" column="question_no" >
			<generator class="increment" />
		</id>
		<many-to-one name="questionType" column="question_type_name"/>
		<property name="questionsTitle" column="questions_title" length="200" />	
	</class>
</hibernate-mapping>

<set name="quesion" inverse="true" cascade="delete">
	<key column="question_type_name"/>
	<one-to-many class="Question"/>
</set>

<many-to-one name="questionType" column="question_type_name"/>

session.beginTransaction();

QuestionType questionType = (QuestionType) session.load(QuestionType.class, "判断题");			
session.delete(questionType);		
session.getTransaction().commit();