This is the parent
<hibernate-mapping>
   <class name="com.file.exchange.vo.Folder" table="FOLDER">
   <id name="id" column="ID" type="java.lang.Integer">
         <generator class="increment"/>
   </id>
   <property name="folder" column="Folder" type="java.lang.String"/>
   <set name="items" cascade="all" lazy="false">
      <key column="Folder_ID" update="true" />
         <one-to-many class="com.file.exchange.vo.Files" />
   </set>
   </class>
</hibernate-mapping>

This is the child

<hibernate-mapping>
   <class name="com.file.exchange.vo.Files" table="FILE">
   <id name="id" column="ID" type="java.lang.Integer">
   <generator class="increment"/>
   </id>
   <property name="name" column="Name" type="java.lang.String"/>
   <property name="type" column="Type" type="java.lang.String"/>
   <property name="size" column="Size" type="java.lang.String"/>
   <property name="date_uploaded" column="Date_UpLoaded" type="java.lang.String"/>
   <property name="folder_id" column="Folder_ID" update="true" insert="true" lazy="false" type="java.lang.Integer"/>
   <property name="user_id" column="User_ID" lazy="false" type="java.lang.Integer"/>
   </class>
</hibernate-mapping>