Ive got Clients and Books.
Clients have a list of Books which they are "borrowing".
This is a <list> with a join table (mappings below).
I've got an index (=IDX) column to manage the list index.

Something very wierd is happening when remove Books from a Client:

Say I add 4 books to the Clients List.
I can then successfully remove the 3rd and 4th books in the list - but not the 1st or 2nd.
(All I can get from the exception is "org.hibernate.exception.GenericJDBCException: Could not execute JDBC batch update").

After I remove either the 3rd or the 4th book - I can then remove the 2nd book - but not the first.
If I remove both the 3rd and 4th books - I can then remove both the 1st and 2nd books.

Can any one give me any tips on why this might happen?

Dave


Hibernate version:
Hibernate 3

Mapping documents:

<hibernate-mapping package="x.y.z.model">

<class name="Client" table="CLIENT" lazy="false">
<id name="id" column="ID" access="field">
<generator class="native"/>
</id>
<property name="name" column="NAME"
access="field" unique="true" not-null="true"/>

<list name="borrowedBooks" access="field" lazy="false" table="CLIENTBOOKS">

<key column="CLIENTID"/>
<index column="IDX"/>
<many-to-many class="Book" column="BOOKID" unique="true"/>

</list>

</class>

</hibernate-mapping>

<hibernate-mapping package="x.y.z.model">

<class name="Book" table="BOOK" lazy="false">
<id name="id" column="ID" access="field">
<generator class="native"/>
</id>
<property name="name" column="NAME"
access="field" unique="true" not-null="true"/>

<property name="status" column="STATUS"
access="field" not-null="true">
<type name="org.hibernate.type.EnumType">
<param name="enumClass">x.y.z.BookStatus</param>
</type>
</property>

<property name="category" column="CATEGORY"
access="field" not-null="true">
<type name="org.hibernate.type.EnumType">
<param name="enumClass">x.y.z.BookCategory</param>
</type>
</property>

</class>

</hibernate-mapping>

DB = HSQLDB (server mode)

It was a unique contraint on CLIENTBOOKS (IDX)