What is wrong with my code, Help me.

Below is my java class, hibernate mapping in hbm.xml. and HQL Query
I need to retrive the top level categories from table, means whose
parentId = 0

Tabel data
id name shortName parentId
1 A a 0
2 B b 0
3 A1 a1 1
4 C c 0
---------------------------------------

package symbio.jobs.businessObjects;

import java.io.Serializable;

import stellar.commons.DropDownItem;
import stellar.commons.businessEntities.BusinessEntity;

/** @author Hibernate CodeGenerator */
public class Category extends BusinessEntity implements Serializable, DropDownItem {

/**
*
*/
private static final long serialVersionUID = 1L;

/** persistent field */
private String name;

/** persistent field */
private String shortName;

/** persistent field */
private Category parentCategory;

/**
* @return Returns the parentCategory.
*/
public Category getParentCategory() {
return parentCategory;
}

/**
* @param parentCategory The parentCategory to set.
*/
public void setParentCategory(Category parentCategory) {
this.parentCategory = parentCategory;
}

/** full constructor */
public Category(String name, String shortName) {
this.name = name;
this.shortName = shortName;
}

/** default constructor */
public Category() {
}

public String getName() {
return this.name;
}

public void setName(String name) {
this.name = name;
}

public String getShortName() {
return this.shortName;
}

public void setShortName(String shortName) {
this.shortName = shortName;
}

public String toString() {
return name;
}


public Object getDisplayString() {
return name;
}

public Object getKey() {
return getId();
}


}

<class name="symbio.jobs.businessObjects.Category" table="categories" >
<id name="id"><generator class="identity"/></id>
<property name="name" type="string" not-null="true" unique="true" />
<property name="shortName" type="string" not-null="true" unique="true" />
<many-to-one name="parentCategory" column="parentId" class="symbio.jobs.businessObjects.Category" />
</class>

(HQL Query)

FROM Category category where category.parentCategory = 0

You don't say exactly what your problem is but it might well stem from the fact that Hibernate doesn't know that a parentId of 0 means that it has no parent. It would be better to have nulls for those items in the column but if not you could set not-found to ignore on the many-to-one and query using something like:-