<class name="Person" table="PERSON">
<id name="id"/>
<property name="sex"/>
<property name="weight"/>
</class>

<class name="Employee" table="EMPLOYEE">
<id name="keyid"/>
<property name="skills"/>
</class>

==============
public class Person
{
String id = null;
String sex = null;
String weight = null;
/* getters and setters */
}

public class Employee extends Person
{
String keyid = null;
String skills = null;
/* getters and setters */
}

===============
When I perform the following query:
Query q = sess.createQuery("select count(*) from Person");
int total = ((Integer)q.uniqueResult()).intValue();

Above HQL statement throws a NonUniqueObjectException. It actually returns two records..... The first record is 0 and the second record is the correct total number of rows.
However if I removed the Employee definition in the mapping file, it works fine without problem.

Any Idea?
I am very new to hibernate, any info would be grateful.
Thanks.

Can you set show_sql="true" and post the sql output?

Sure, Hibernate issues two seperate selects (one for Person, one for Employee). Try maybe using union-subclass to map this inheritence instead.

Essentially Hibernate is doing:



and returning these as lists. SQL has tables, and select count(*) from a table in SQL will always return exactly one row, but HQL is based on objects, which don't always correspond with tables.

To put it another way, if you did a HQL query like this:


you would select every object in the system. Of course that query would involve every table in the system. You are basically doing which must look at both Person and Employee.