hibernate表格外键引用自己

<class   name="mypack.Category"   table="CATEGORIES"   > 
        <id   name="id"   type="long"   column="ID"> 
            <generator   class="increment"/> 
        </id>         <property   name="name"   type="string"   > 
                <column   name="NAME"   length="15"   /> 
        </property>         <set   
                name="childCategories" 
                cascade="save-update" 
                inverse="true" 
                > 
                <key   column="CATEGORY_ID"   /> 
                <one-to-many   class="mypack.Category"   /> 
          </set>             <many-to-one 
                name="parentCategory" 
                column="CATEGORY_ID" 
                class="mypack.Category" 
              />     </class>