I created a list and defined an index column (I read that it is mandatory to define an index for a list):

<list name="fields" lazy="false" fetch="subselect" cascade="all,delete-orphan">
<key column="LIST_ID"/>
<index column="INDEX" type="long"/>
<one-to-many class="Field"/>
</list>

In the Field class, I set values in the 'index' property. However, I can see that these values are overridden.
Is there a way to manage the index independently - that Hibernate will not override the property?

In the definition of the Field object mapping, is the index type set to assigned?

It is set only as a property:

<property name="index" type="long" column="INDEX" insert="false" update="false"/>

In the mapping for the Field object, do you have something like this?

<class name="Field" table="Field_table">
<id name="index" type="long" column="INDEX">
<generator class="assigned"/>
</id>
</class>

I ask because previously you had stated you were assigning a value to the index for the FIeld object.