Criteria returning multiple copies of same object

jayhawk · **Posted:** Fri Jan 26, 2007 4:44 pm

The following 2 sections of code are returning a different number of results, which appears to be a Hibernate bug. Is there any reason (odd config, etc) that this might not be a bug?

Option 1

Code:

Criteria crit = session.createCriteria(treeDefClass);
List<?> results = crit.list();

Option 2

Code:

Query q = session.createQuery("from " + treeDefClass.getSimpleName() + " as def");
List<?> results = q.list();

The first option returns 400 copies of the same object (same in the sense of the Java = operator, meaning same identity, not just object equality). The second option returns the correct result, 1 object.

Any ideas?

In case it matters...
I'm using Hibernate 3.2.1 GA and Annotations 3.2.1 GA on a Windows XP SP 2 host running a MySQL 5.0.27 DB.

jayhawk · **Posted:** Wed Jan 31, 2007 2:49 pm

This appears to be related to EAGER fetching. I setup my DB to have 1 'Parent' record and 4 'Child' records, based on the following two classes...

Code:

package datamodel;

import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.OneToMany;

/**
 *
 * @code_status Alpha
 * @author jayhawk
 */
@Entity(name="parent")
public class Parent
{
    protected Long id;
    protected String name;
    protected Set<Child> children;
    
    @Id
    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;
    }
    
    @OneToMany(mappedBy="parent", fetch=FetchType.EAGER)
    public Set<Child> getChildren()
    {
        return children;
    }
    public void setChildren(Set<Child> children)
    {
        this.children = children;
    }
}

package datamodel;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

/**
 *
 * @code_status Alpha
 * @author jayhawk
 */
@Entity(name="child")
public class Child
{
    protected Long id;
    protected String name;
    protected Parent parent;
    
    @Id
    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;
    }
    
    @ManyToOne
    public Parent getParent()
    {
        return parent;
    }
    public void setParent(Parent parent)
    {
        this.parent = parent;
    }
}

When I leave fetch=FetchType.EAGER on the getChildren() method, a Criteria query returns 4 results from my DB (one for each child). Using show_sql, I see that Hibernate is doing a join.

When I remove fetch=FetchType.EAGER and let the system default to LAZY, I get only 1 result, the proper number.

jayhawk · **Posted:** Wed Jan 31, 2007 3:12 pm

I found another posting about this problem. It suggested putting...

Code:

criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);

after creating each Criteria. This seems to work, but I have no idea what it's actually doing. I'll have to spend some time figuring that out.

Is this safe to do on ALL Criteria queries?

dharmendra.pandey · **Posted:** Thu Feb 01, 2007 3:09 am

Hi jayhawk,

Have you extend Parent Or Child and mapped these with other HBM file

jayhawk · **Posted:** Thu Feb 01, 2007 11:16 am

dharmendra.pandey wrote:

Have you extend Parent Or Child and mapped these with other HBM file

No I haven't. Parent and Child are both as given above, and no subclasses exist for either of them.

gutzeit · **Joined:** Mon Aug 28, 2006 12:01 pm **Posts:** 11

Putting criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY) on each query will cancel the pagination feature, since it filters the results on the hibernate side and not on the DB, while the pagination works on the DB side.

Is it safe to use it, if you do not need pagination.

I have the same problem with the same results returned by the Criteria API queries, and I have to use eager fetching due the nature of my application. Still found no proper solution.

There is a feature request opened for a few years to add "distinct" option to the Criteria API, but no one seems to care.

christian · **Posted:** Fri Feb 02, 2007 5:24 am

http://www.hibernate.org/117.html#A12

You can't do SQL row-based pagination when you do outer join fetching. No "distinct" keyword is going to help you with that. Just look at the SQL resultset.

gutzeit · **Joined:** Mon Aug 28, 2006 12:01 pm **Posts:** 11

Is there a way not to use "OUTER" join when working with Criteria API ?

christian · **Posted:** Sat Feb 03, 2007 3:52 am

Sure, you can use an inner join (inner join collection fetching rarely makes sense). But its the same problem, because the resultset also contains duplicates that conflict with row-based limits...

gutzeit · **Joined:** Mon Aug 28, 2006 12:01 pm **Posts:** 11

Just to make it clear, THE ONLY way to use pagination with eager fetching, is by setting @Fetch(value = FetchMode.SELECT) ?