Example
Table User (fields: name, desc)
Table Items (fields: itemname, desc)
Table User_Item_Crosswalk = Crosswalk between A and B.

In User, I assign instances of Items through the crosswalk table
Everything works fine in hibernate. so lets say
User1 has Items A, B, and C

However, if I change any property of an item (the name or description, it deletes the reference that User1 has of that item. (ie it deletes the record from the crosswalk table)

Any idea why this would occur?
The only property I have on the .hbm.xml on the set attribute is to lazy="true"

Can you post the relevant Hibernate mappings?

well my example was a dumb'down version of what I was coding. Here is the maping file for the user

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
<class
name="SecurityUserDO"
table="security_user">

<id
name="id"
column="user_id"
type="java.lang.Long">
<generator class="increment"/>
</id>

<property name="userName" column="user_name" type="string" not-null="true" />
<property name="password" column="user_password" type="string" not-null="true" />

<property name="firstName" column="first_name" type="string" not-null="true" />
<property name="lastName" column="last_name" type="string" not-null="true" />
<property name="email" column="email" type="string" not-null="true" />

<property name="inactive" column="inactive" type="boolean" not-null="true" />
<property name="system" column="system" type="boolean" not-null="true" />

<property name="simpleSearchString" column="simple_search" type="string" not-null="true" />

<property name="createdBy" column="created_by" type="string" not-null="true" />
<property name="createdStamp" column="created_stamp" type="timestamp" not-null="true" />
<property name="updatedBy" column="updated_by" type="string" not-null="true" />
<property name="updatedStamp" column="updated_stamp" type="timestamp" not-null="true" />

<set name="securityPermissions" table="security_user_permission_crswlk" lazy="true">
<key column="user_id" />
<many-to-many column="permission_id" class="SecurityPermissionDO" />
</set>

<set name="securityRoles" table="security_user_role_crswlk" lazy="true">
<key column="user_id" />
<many-to-many column="role_id" class="SecurityRoleDO" />
</set>
</class>
</hibernate-mapping>


And then for the role (which when edited, is being removed from the user)

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
<class
name="SecurityRoleDO"
table="security_role">

<id
name="id"
column="role_id"
type="java.lang.Long">
<generator class="increment"/>
</id>

<property name="roleName" column="role_name" type="string" not-null="true"/>
<property name="roleDesc" column="role_desc" type="string" not-null="true"/>

<property name="inactive" column="inactive" type="boolean" not-null="true" />
<property name="system" column="system" type="boolean" not-null="true" />

<property name="simpleSearchString" column="simple_search" type="string" not-null="true" />

<property name="createdBy" column="created_by" type="string" not-null="true" />
<property name="createdStamp" column="created_stamp" type="timestamp" not-null="true" />
<property name="updatedBy" column="updated_by" type="string" not-null="true" />
<property name="updatedStamp" column="updated_stamp" type="timestamp" not-null="true" />


<set name="securityUsers" table="security_user_role_crswlk" lazy="true" >
<key column="role_id" />
<many-to-many column="user_id" class="SecurityUserDO" />
</set>

<set name="securityPermissions" table="security_role_permission_crswlk" >
<key column="role_id" />
<many-to-many column="permission_id" class="SecurityPermissionDO" />
</set>
</class>
</hibernate-mapping>

On doing an update to Role, the following stastements are debug 'd

15:10:48,464 DEBUG BasicCollectionPersister:479 - Deleting collection: [SecurityRoleDO.securityUsers#8]
15:10:48,464 DEBUG BatcherImpl:204 - about to open: 0 open PreparedStatements, 0 open ResultSets
15:10:48,464 DEBUG SQL:230 - delete from security_user_role_crswlk where role_id=?
Hibernate: delete from security_user_role_crswlk where role_id=?

The Javadoc for the Set API has this to say:



Could you be running afoul of this stipulation of the Set contract?

—ml—

Ahhh i figured it out.
When I was editing the role, the list of users was set to null, thus it removed all the references to user.