Hi, can anybody help? I got an error when start running the application.
Initial SessionFactory creation failed.org.hibernate.MappingException: Repeated column in mapping for entity: com.hibernate.entities.Item column: seller_id (should be mapped with insert="false" update="false")

My mapping files:
<class name="Item" table="item" lazy="false">
<id name="itemId" column="item_id" type="long">
<generator class="sequence">
<param name="sequence">item_seq</param>
</generator>
</id>
<property name="description" column="description"/>
<property name="initialPrice" column="initial_price"/>
<many-to-one name="seller" column="seller_id" class="Seller" />
</class>

<class name="Seller" table="seller" batch-size="1" >
<id name="sellerId" column="seller_id" type="long">
<generator class="sequence">
<param name="sequence">seller_seq</param>
</generator>
</id>

<property name="name" column="name"/>
<set name="items" cascade="save-update" lazy="false">
<key column="seller_id" not-null="true"/>
<one-to-many class="Item"/>
</set>
</class>

I know that it's because I use not-null="true", so Hibernate requires me to set insert="false" update="false" on the <many-to-one name="seller" column="seller_id" class="Seller" />. But, I would like to know the reason why does Hibernate have to generate the exception for requiring us to set the parameters?