I have two classes, Test2 and Test3. Test2 has an attribute test3 that is an instance of Test3. In other words, I have a unidirectional OneToOne association, with test2 having a reference to test3.
When I select Test2 from the db, I can see that a separate select is being made to get the details of the associated test3 class. This is the famous 1+N selects problem.
To fix this to use a single select, I am trying to use the fetch=join annotation, which I understand to be @Fetch(FetchMode.JOIN)
However, with fetch set to join, I still see separate selects. Here are the relevant portions of my setup..
hibernate.cfg.xml:
<property name="max_fetch_depth">2</property>
Test2:
public class Test2 {
@OneToOne (cascade=CascadeType.ALL , fetch=FetchType.EAGER)
@JoinColumn (name="test3_id")
@Fetch(FetchMode.JOIN)
public Test3 getTest3() {
return test3;
}
NB I set the FetchType to EAGER out of desperation, even though it defaults to EAGER anyway for OneToOne mappings, but it made no difference.
Thanks for any help!
Edit: I've pretty much given up on trying to use FetchMode.JOIN - can anyone confirm that they have got it to work ie produce a left outer join? In the docs I see that "Usually, the mapping document is not used to customize fetching. Instead, we keep the default behavior, and override it for a particular transaction, using left join fetch in HQL"
If I do a left join fetch instead:
query = session.createQuery("from Test2 t2 left join fetch t2.test3");
then I do indeed get the results I want - ie a left outer join in the query.
Edit number 2:
Guys, thank you so much for your responses. Now I want to get to the bottom of this. I usually find that when I investigate something, I end up learning a lot more than I thought I would.
One thing I've learned already - I was running on old builds of hibernate because I didn't realize that the maven repository was out of date. Now I'm hooked up to the jboss repository too, and I have the latest versions of hibernate and hibernate annotations - 3.5.1-Final in both cases.
I've set up a small test case that simplifies it as much as I can - I'm still seeing the problem in 3.5.1-Final, tho' I'm 99% certain it's just something stupid I'm not setting up right, especially Ross, given that you got it to work (thanks for taking the time to try it by the way)
So I have these classes (full text this time)
Class A
package com.play.hibernate2;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import org.hibernate.annotations.Fetch;
import org.hibernate.annotations.FetchMode;
@Entity
public class A {
private Integer id;
private B b;
public A() {
super();
}
@Id
@GeneratedValue
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
@OneToOne (cascade=CascadeType.ALL)
@Fetch(FetchMode.JOIN)
public B getB() {
return b;
}
public void setB(B b) {
this.b = b;
}
}
Class B
package com.play.hibernate2;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
@Entity
public class B {
private Integer id;
public B() {
super();
}
@Id
@GeneratedValue
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
}
My whole hibernate.cfg.xml
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<!-- Database connection settings -->
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<!-- <property name="connection.driver_class">com.p6spy.engine.spy.P6SpyDriver</property> -->
<property name="connection.url">jdbc:mysql://localhost:3306/play</property>
<property name="connection.username">play</property>
<property name="connection.password">play</property>
<!-- JDBC connection pool (use the built-in) -->
<property name="connection.pool_size">1</property>
<!-- SQL dialect -->
<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
<!-- Enable Hibernate's automatic session context management -->
<property name="current_session_context_class">thread</property>
<!-- Disable the second-level cache -->
<property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
<!-- Echo all executed SQL to stdout -->
<property name="show_sql">true</property>
<property name="generate_statistics">true</property>
<!--
<property name="cache.use_structured_entries">true</property>
<property name="cache.use_query_cache">true</property>
-->
<property name="format_sql">true</property>
<property name="use_sql_comments">true</property>
<!-- I think this may fix my individual requests for OneToOne problem -->
<property name="max_fetch_depth">2</property>
<!-- <property name="default_batch_fetch_size">10</property> -->
</session-factory>
</hibernate-configuration>
The testing class
package com.play.hibernate2;
import java.util.List;
import java.util.Map;
import org.hibernate.FlushMode;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
public class RunTests4 {
private SessionFactory sessionFactory;
public static void main(String[] args){
RunTests4 d = new RunTests4();
d.run3();
}
public void run3(){
Session session = getSession();
session.beginTransaction();
createEntities(session);
session.getTransaction().commit();
System.out.println("NOW WITH A NEW TRANSACTION");
session = getSession();
session.beginTransaction();
Query query = session.createQuery("from A");
List results = query.list();
for (int i=0; i<results.size(); i++){
System.out.println("Row "+i+" was:");
A a = (A)results.get(i);
System.out.println("Result "+i);
System.out.println(a.toString());
}
session.getTransaction().commit();
}
public void createEntities(Session session){
for (int i=0; i<2; i++){
A a = new A();
B b = new B();
a.setB(b);
session.save(a);
}
}
public Session getSession(){
if (sessionFactory == null){
AnnotationConfiguration config = new AnnotationConfiguration();
config.addAnnotatedClass(A.class);
config.addAnnotatedClass(B.class);
config.configure();
new SchemaExport(config).create(true,true);
sessionFactory = config.buildSessionFactory();
}
Session session = sessionFactory.getCurrentSession();
return session;
}
}
And finally the log output showing the extra selects to get back the associated class
2 [main] INFO org.hibernate.cfg.annotations.Version - Hibernate Annotations 3.5.1-Final
23 [main] INFO org.hibernate.cfg.Environment - Hibernate 3.5.1-Final
28 [main] INFO org.hibernate.cfg.Environment - hibernate.properties not found
32 [main] INFO org.hibernate.cfg.Environment - Bytecode provider name : javassist
37 [main] INFO org.hibernate.cfg.Environment - using JDK 1.4 java.sql.Timestamp handling
160 [main] INFO org.hibernate.annotations.common.Version - Hibernate Commons Annotations 3.2.0.Final
176 [main] INFO org.hibernate.cfg.Configuration - configuring from resource: /hibernate.cfg.xml
176 [main] INFO org.hibernate.cfg.Configuration - Configuration resource: /hibernate.cfg.xml
313 [main] INFO org.hibernate.cfg.Configuration - Configured SessionFactory: null
338 [main] INFO org.hibernate.dialect.Dialect - Using dialect: org.hibernate.dialect.MySQLDialect
462 [main] INFO org.hibernate.cfg.AnnotationBinder - Binding entity from annotated class: com.play.hibernate2.Test2
545 [main] INFO org.hibernate.cfg.annotations.EntityBinder - Bind entity com.play.hibernate2.Test2 on table Test2
649 [main] INFO org.hibernate.cfg.AnnotationBinder - Binding entity from annotated class: com.play.hibernate2.Test3
650 [main] INFO org.hibernate.cfg.annotations.EntityBinder - Bind entity com.play.hibernate2.Test3 on table Test3
651 [main] INFO org.hibernate.cfg.AnnotationBinder - Binding entity from annotated class: com.play.hibernate2.A
651 [main] INFO org.hibernate.cfg.annotations.EntityBinder - Bind entity com.play.hibernate2.A on table A
653 [main] INFO org.hibernate.cfg.AnnotationBinder - Binding entity from annotated class: com.play.hibernate2.B
653 [main] INFO org.hibernate.cfg.annotations.EntityBinder - Bind entity com.play.hibernate2.B on table B
678 [main] INFO org.hibernate.cfg.AnnotationConfiguration - Hibernate Validator not found: ignoring
687 [main] INFO org.hibernate.tool.hbm2ddl.SchemaExport - Running hbm2ddl schema export
688 [main] INFO org.hibernate.tool.hbm2ddl.SchemaExport - exporting generated schema to database
691 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - Using Hibernate built-in connection pool (not for production use!)
691 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - Hibernate connection pool size: 1
698 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - autocommit mode: false
711 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - using driver: com.mysql.jdbc.Driver at URL: jdbc:mysql://localhost:3306/play
711 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - connection properties: {user=play, password=****}
alter table A
drop
foreign key FK412E010759
alter table Test2
drop
foreign key FK4CF5DC04B7E1B79
drop table if exists A
drop table if exists B
drop table if exists Test2
drop table if exists Test3
create table A (
id integer not null auto_increment,
b_id integer,
primary key (id)
)
create table B (
id integer not null auto_increment,
primary key (id)
)
create table Test2 (
id integer not null auto_increment,
name varchar(255),
value integer not null,
test3_id integer,
primary key (id)
)
create table Test3 (
id integer not null auto_increment,
name varchar(255),
value integer not null,
primary key (id)
)
alter table A
add index FK412E010759 (b_id),
add constraint FK412E01
