Hi all,

I have 5 tables in postgres database.

CREATE TABLE tasks
(
task_id smallint NOT NULL,
description character varying(50),
CONSTRAINT pk_task PRIMARY KEY (task_id)
)


CREATE TABLE roles
(
role_id smallint NOT NULL,
description character varying(25) NOT NULL,
CONSTRAINT pk_roles PRIMARY KEY (role_id)
)

CREATE TABLE role_tasks
(
role_id smallint NOT NULL,
task_id smallint NOT NULL,
CONSTRAINT pk_role_tasks PRIMARY KEY (role_id, task_id),
CONSTRAINT fk_role_tasks_ref_roles FOREIGN KEY (role_id)
REFERENCES roles (role_id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT fk_role_tasks_ref_tasks FOREIGN KEY (task_id)
REFERENCES tasks (task_id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
)


CREATE TABLE users
(
user_id character varying(25) NOT NULL,
"name" character varying(100),
"password" character varying(25),
role_id smallint NOT NULL,
CONSTRAINT pk_users PRIMARY KEY (user_id),
CONSTRAINT fk_users_ref_roles FOREIGN KEY (role_id)
REFERENCES roles (role_id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT uq_user UNIQUE (user_id, role_id)
)


CREATE TABLE user_tasks
(
user_id character varying(25) NOT NULL,
role_id smallint NOT NULL,
task_id smallint NOT NULL,
CONSTRAINT pk_user_tasks PRIMARY KEY (user_id, role_id, task_id),
CONSTRAINT fk_user_task_ref_user FOREIGN KEY (user_id, role_id)
REFERENCES users (user_id, role_id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT fk_user_tasks_ref_role_tasks FOREIGN KEY (role_id, task_id)
REFERENCES role_tasks (role_id, task_id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
)


Hibernate mapping --

<class name="com.stp.dto.ac.Task" table="TASKS">
<meta attribute="class-description">This class contains task details.</meta>
<id name="taskId" type="int" column="TASK_ID">
<generator class="assigned" />
</id>
<property name="description" type="string" not-null="true" column="DESCRIPTION" />
</class>




<class name="com.stp.dto.ac.Role" table="ROLES">
<meta attribute="class-description">This class contains role details.</meta>
<id name="roleId" type="int" column="ROLE_ID">
<generator class="assigned" />
</id>
<property name="description" type="string" not-null="true" column="DESCRIPTION" />
<set name="roleTasks" table="ROLE_TASKS" cascade="all" >
<key column="ROLE_ID" not-null="false"/>
<many-to-many column="TASK_ID" unique="true" class="com.stp.dto.ac.Task" />
</set>
</class>



<class name="com.stp.dto.ac.User" table="USERS">
<meta attribute="class-description">This class contains user details.</meta>
<id name="userId" type="string" column="USER_ID">
<generator class="assigned" />
</id>
<property name="roleId" type="int" not-null="true" insert="false" update="false" column="ROLE_ID" />
<many-to-one name="role" fetch="join" class="com.stp.dto.ac.Role" column="ROLE_ID" insert="true"
update="true" cascade="none" not-null="true"/>
<property name="name" type="string" not-null="true" column="NAME" />
<property name="password" type="string" not-null="true" column="PASSWORD" />


<properties name="aa" insert="false" unique="true" update="false">
<property name="userId" type="string" column="USER_ID" insert="false" update="false"></property>
<property name="roleId" type="int" column="ROLE_ID" insert="false" update="false"></property>
</properties>
<set name="userTasks" table="USER_TASKS" cascade="none" >
<key property-ref="aa">
<column name="USER_ID" ></column>
<column name="ROLE_ID"></column>
</key>
<many-to-many column="TASK_ID" unique="true" class="com.stp.dto.ac.Task">

</many-to-many>
</set>
</class>


Here I am mapping USER_TASKS to user using composite unique constraint on columns role_id and user id using property-ref.

But when I query or insert data using hibernate it throws this exception -
java.lang.ClassCastException: com.stp.dto.ac.User cannot be cast to java.lang.String


query code snippet -
queryString = new StringBuilder();
queryString.append("from User u left join fetch u.userTasks ut ");
Query query = session.createQuery(queryString.toString());
userSet = new LinkedHashSet(query.list());

please give me a suggestion to come out of this error

Thanks,
Sujnan