Association of many collections to a single entity

drj · **Posted:** Mon Apr 04, 2005 11:00 am

Hibernate version: 2.1.8
Name and version of the database you are using: Postgres 8.0
Hi,

Is there any way to manually fetch a collection-type association and attach it to a set of entities so that you could get around the single collection fetching limitation?

For example:

I have an entity A which has two associations (Bee and Cee) both mapped as lazy collections (one-to-many from A)

Code:

(Bee) *---------1 (A) 1---------* (Cee)

Currently it is only possibly to perform a single fetch join so I do the following:

Code:

List aasWithBeesInitialised = session.createQuery(
    "from A ac "+
    "left join fetch a.bee b")
    .list();


List ceesWithAasInitialised = session.createQuery(
    "from Cee c "
     "left join fetch c.a")
    .list();

Now somehow (Yes - i know how to do this manually - but I'm looking for a transparent solution) attach the cees to a.

I suppose that I'm barking up the tree of 'transparent re-association' within the session scope. Any ideas?

TIA

anthony · **Posted:** Mon Apr 04, 2005 12:08 pm

change to

Code:

List aasWithBeesInitialised = session.createQuery( 
    "from A ac "+ 
    "left join fetch a.bee b") 
    .list(); 


List aasWithCeesInitialised = session.createQuery( 
    "from A ac "+ 
    "left join fetch a.cee c") 
    .list();  

and all will be loaded, you can continue working with aasWithBeesInitialised or aasWithCeesInitialised

drj · **Posted:** Mon Apr 04, 2005 1:28 pm

Thanks Anthony - works like a charm.

For anyone that is interested - here is a test case that proves it

Code:

package test;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import net.sf.hibernate.Hibernate;
import net.sf.hibernate.Session;
import net.sf.hibernate.SessionFactory;
import net.sf.hibernate.Transaction;
import net.sf.hibernate.cfg.Configuration;
import junit.framework.TestCase;

public class ABCTest extends TestCase {

   
    public ABCTest() {
        super();
    }

    public ABCTest(String arg0) {
        super(arg0);
    }

    public void testIt() throws Exception {
        SessionFactory sf = new Configuration().configure().buildSessionFactory();
        insertData(sf);
        queryData(sf);
    }
    
    private void insertData(SessionFactory sf) throws Exception {
        Session session = sf.openSession();
        try {
            Transaction tx = session.beginTransaction();
            
            Aaa a = new Aaa();
            a.setName("a");
            
            Bee b1 = new Bee();
            b1.setName("b1");
            
            Bee b2 = new Bee();
            b2.setName("b2");
            
            List bees = new ArrayList();
            bees.add(b1);
            bees.add(b2);
            a.setBees(bees);
            
            Cee c1 = new Cee();
            c1.setName("c1");
            
            Cee c2 = new Cee();
            c2.setName("c2");
            
            List cees = new ArrayList();
            cees.add(c1);
            cees.add(c2);
            a.setCees(cees);
            
            session.save(a);
            tx.commit();
        }
        finally {
            session.close();
        }
    }
    
    private void queryData(SessionFactory sf) throws Exception {
        Session session = sf.openSession();
        try {
            session.createQuery(
                    "from Aaa a "+
                    "left join fetch a.bees b")
                    .list();           
            
            List aasWithCeesInitialised = session.createQuery(
                    "from Aaa a "+
                    "left join fetch a.cees c")
                    .list();
            
            for (Iterator iter = aasWithCeesInitialised.iterator(); iter.hasNext(); ) {
                Aaa a = (Aaa)iter.next();
                assertTrue(Hibernate.isInitialized(a));
                assertTrue(Hibernate.isInitialized(a.getBees()));
                assertTrue(Hibernate.isInitialized(a.getCees()));
            }
            
        }
        finally {
            session.close();
        }
    }
}

Code:

package test;

import java.util.Collection;
/**
 * @hibernate.class 
 *      table = "aaa"
 */
public class Aaa {
    
    private Integer id;
    private String name;
    
    private Collection bees;
    private Collection cees;

    public Aaa() {
        super();
    }
    
    /**
     * @hibernate.id 
     *      generator-class = "native"
     *      unsaved-value = "null"
     *      type = "int"
     */
    public Integer getId() { return id; }
    public void setId(Integer id) { this.id = id; }    
    
    /**
     * @hibernate.property
     *      not-null = "true"
     */
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    
    /**
     * @hibernate.bag 
     *      cascade = "all"
     *      lazy = "true"
     * @hibernate.collection-key 
     *      column = "a_id"
     * @hibernate.collection-one-to-many 
     *      class = "test.Bee"
     */
    public Collection getBees() { return bees; }
    public void setBees(Collection bees) { this.bees = bees; }
    
    /**
     * @hibernate.bag 
     *      cascade = "all"
     *      lazy = "true"
     * @hibernate.collection-key 
     *      column = "a_id"
     * @hibernate.collection-one-to-many 
     *      class = "test.Cee"
     */
    public Collection getCees() { return cees; }
    public void setCees(Collection cees) { this.cees = cees; }    
}

Code:

package test;
/**
 * @hibernate.class 
 *      table = "bee"
 */
public class Bee {
    
    private Integer id;
    private String name;

    public Bee() {
        super();
    }
    
    /**
     * @hibernate.id 
     *      generator-class = "native"
     *      unsaved-value = "null"
     *      type = "int"
     */
    public Integer getId() { return id; }
    public void setId(Integer id) { this.id = id; }    
    
    /**
     * @hibernate.property
     *      not-null = "true"
     */
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
}

Code:

package test;
/**
 * @hibernate.class 
 *      table = "cee"
 */
public class Cee {
    
    private Integer id;
    private String name;

    public Cee() {
        super();
    }
    /**
     * @hibernate.id 
     *      generator-class = "native"
     *      unsaved-value = "null"
     *      type = "int"
     */
    public Integer getId() { return id; }
    public void setId(Integer id) { this.id = id; }    
    
    /**
     * @hibernate.property
     *      not-null = "true"
     */
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
}