I have the parent/child type relation for categories with the lazy initialization of the parentCategory and childCategories as default in the mapping file.

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="by.hibernate.app.model.Category" table="CATEGORY">
<id name="id" column="CATEGORY_ID">
<generator class="native"/>
</id>
<property name="name" column="NAME"/>
<many-to-one
name="parentCategory"
class="by.hibernate.app.model.Category"
column="PARENT_CATEGORY_ID"
cascade="none"/>
<set
name="childCategories"
table="CATEGORY"
cascade="all"
inverse="true" lazy="true">
<key column="PARENT_CATEGORY_ID"/>
<one-to-many class="by.hibernate.app.model.Category"/>
</set>
</class>
</hibernate-mapping>

Hibernate version: 3.1.3

I need to show all the categories on the page at once.

I tried to achive that with Criteria by setting FetchMode.JOIN as follows:

Criteria criteria = session.createCriteria(Category.class);
criteria.setFetchMode("parentCategory", FetchMode.JOIN);
criteria.setFetchMode("childCategories", FetchMode.JOIN);
criteria.add(Expression.isNull("parentCategory"));
Set categories = new HashSet(criteria.list());

I got parent categories with the collection of child categories. Unfortunately, each item in the childCategories collection has an uninitialized childCategories collection. I'll give an example:

+Auto - parent element
--+Audi - child element
----+Audi 100 - child element
----+Audi 80 - child element
--+Mazda - child element
----+Mazda 6 - child element
----+Mazda 3 - child element
+Computres - parent element
--+Dell - child element
----+Laptop - child element

I got collection of 2 elemnts: Auto and Computers with childCategories containing (Audi, Mazda) and (Dell) respectively. The problem is that the childCategories collection of the Audi, Mazda and Dell objects is uninitialized - throws LazyInitializationException.

I tried to do the same with HQL like:

Query query = session.createQuery("from Category c left join fetch c.parentCategory left join fetch c.childCategories where c.parentCategory is null");
Set categories = new HashSet(query.list());

and got the same result.

I found that I could set the lazy to false as default in the mapping :

<set
name="childCategories"
table="CATEGORY"
cascade="all"
inverse="true" lazy="false">
<key column="PARENT_CATEGORY_ID"/>
<one-to-many class="by.hibernate.app.model.Category"/>
</set>

and all started working without setFetchMode for the childCategories property:

Criteria criteria = session.createCriteria(Category.class);
criteria.setFetchMode("parentCategory", FetchMode.JOIN);
criteria.add(Expression.isNull("parentCategory"));
Set categories = new HashSet(criteria.list());

However this approach can't be used because the lazy initialization is used in another usecases. Moreover, if lazy="false" is default, there is no way to set another fetch mode for Criteria, say FetchMode.SELECT (it seems to be a bug in Hibernate).

Any ideas how to resolve this issue?

Attaching Category java file:

package by.hibernate.app.model;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

public class Category implements Serializable {
private Long id;
private String name;
private Category parentCategory;
private Set childCategories = new HashSet();

public Category() {
}

public Category(Long id, String name) {
this.id = id;
this.name = name;
}

public Category(String name) {
this.name = name;
}

public Long getId() {
return id;
}

public void setId(Long id) {
this.id = id;
}

public String getName() {
return name;
}

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

public Set getChildCategories() {
return childCategories;
}

public void setChildCategories(Set childCategories) {
this.childCategories = childCategories;
}

public Category getParentCategory() {
return parentCategory;
}

public void setParentCategory(Category parentCategory) {
this.parentCategory = parentCategory;
}

public void addChildCategory(Category childCategory) {
if (childCategory == null)
throw new IllegalArgumentException("Null child category!");

if (childCategory.getParentCategory() != null)
childCategory.getParentCategory().getChildCategories().remove(childCategory);

childCategory.setParentCategory(this);
childCategories.add(childCategory);
}
}