I have two entities, User and Group, with many-to-many relation:

-------------------------------------------------------------------------------------------------- User.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="test.hibernate">
<class name="User" table="`USER`">
<id name="id" type="long" unsaved-value="null">
<column name="USER_ID" not-null="true"/>
<generator class="native"/>
</id>

<property name="login">
<column name="LOGIN" not-null="true" length="255"/>
</property>

<bag name="groups" table="USER_GROUP" lazy="false" cascade="none">
<key column="USER_ID"/>
<many-to-many class="Group" column="GROUP_ID"/>
</bag>
</class>
</hibernate-mapping>

-------------------------------------------------------------------------------------------------- Group.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="test.hibernate">
<class name="Group" table="`GROUP`">
<id name="id" type="long" unsaved-value="null">
<column name="GROUP_ID" not-null="true"/>
<generator class="native"/>
</id>

<property name="name">
<column name="GROUPNAME" not-null="true" length="100"/>
</property>

<bag name="users" table="USER_GROUP" lazy="true" inverse="true" cascade="all-delete-orphan">
<key column="GROUP_ID"/>
<many-to-many class="User" column="USER_ID"/>
</bag>
</class>

<query name="Group.select.by.login" cacheable="true"><![CDATA[
select user.groups from User user where user.login=?
]]>
</query>
</hibernate-mapping>
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- test.hibernate.User and test.hibernate.Group classes are just simple beans.

In Group.hbm.xml there is a query called "Group.select.by.login", it's intended to be cached. So I add corresponding properties to Hibernate configuraition:
-------------------------------------------------------------------------------------------------- properties.put("hibernate.cache.provider_class", "org.hibernate.cache.EhCacheProvider");
properties.put("hibernate.cache.use_query_cache", "true");
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Configuration has no extra parameters.

Then I'm trying to execute the query two times:
-------------------------------------------------------------------------------------------------- test fragment
SessionFactory sessionFactory = configuration.buildSessionFactory();
Session session = null;

try {
session = sessionFactory.openSession();
Query query = session.getNamedQuery("Group.select.by.login");
List<Group> groups;

groups = query.setParameter(0, "admin").list(); // +++++++++++++++This list() returns list of two Group objects, ok +++++++++++++++
System.out.println("-----------------------------------------------------------------------------------");
for (Group group : groups) {
System.out.println(group.getName());
}
System.out.println("-----------------------------------------------------------------------------------");

groups = query.setParameter(0, "admin").list(); // +++++++++++++++This list() returns list of two nulls +++++++++++++++
System.out.println("-----------------------------------------------------------------------------------");
for (Group group : groups) {
System.out.println(group.getName());
}
System.out.println("-----------------------------------------------------------------------------------");
} finally {
if (session != null) {
session.close();
}
sessionFactory.close();
}
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The first query returns list of, in my case, two groups. The second query returns list of two nulls instead of the same list.

I've investigated the problem, and found the following:

Query return value is "user.groups", and during query analysis (org.hibernate.hql.ast.QueryTranslatorImpl:160) query return type is defined as "org.hibernate.type.BagType(test.hibernate.User.groups)". This seems to be the problem, as during query put operation org.hibernate.CollectionType.disassemble is called (org.hibernate.cache.StandardQueryCache:80), which simply returns null as owner is null.

If this query is not a misuse, then I think, something is to be done at the time of analysis, so that return type be somewhat different.

Thanks.