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Answer 1

+2 A:

Hi,

I created a very simple application to test the scenario you are getting and your code should work (it is working for me). The only thing I have tried that will give me multiple select statements is setting max_fetch_depth to 0. If set to 2 (or not configured) I get the left outer join in my query. What version of hibernate are you using? I am using 3.4.0.GA.

EDIT: Below is the simple application I used (with the same versions mentioned by Pascal):

cfg:

<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">org.hsqldb.jdbcDriver</property>
        <property name="hibernate.connection.url">jdbc:hsqldb:hibscribs</property>
        <property name="hibernate.connection.username">sa</property>
        <property name="hibernate.connection.password"></property>
        <property name="hibernate.dialect">org.hibernate.dialect.HSQLDialect</property>
        <property name="show_sql">true</property>
        <property name="format_sql">true</property>
        <property name="hbm2ddl.auto">create-drop</property>
        <property name="current_session_context_class">thread</property>
        <!-- property name="max_fetch_depth">0</property--><!-- uncomment to see where 2 selects are used instead of join -->

        <mapping class="com.mydomain.bo.Person" />
        <mapping class="com.mydomain.bo.Phone" />

    </session-factory>
</hibernate-configuration>

Person entity -- kept it simple only have @OneToOne, adding JoinColumn, etc made no difference.

@Entity
@Table(name="person")
public class Person {
    private Long id;
    private String name;
    private Phone phone;

    @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;
    }

    @OneToOne(cascade=CascadeType.ALL)
    public Phone getPhone() {
        return phone;
    }

    public void setPhone(Phone phone) {
        this.phone = phone;
    }   
}

.

@Entity
@Table(name="phone")
public class Phone {
    private Long id;
    private String number;

    @Id
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }

    public String getNumber() {
        return number;
    }
    public void setNumber(String number) {
        this.number = number;
    }
}

Simple test:

SessionFactory session = HibernateUtil.getSessionFactory();
Session sess = session.getCurrentSession();
Transaction tx = sess.beginTransaction();

Phone phone = new Phone();
phone.setId(1L);
phone.setNumber("1234567");

Person person = new Person();
person.setId(1L);
person.setName("Bob");
person.setPhone(phone);

sess.save(person);

tx.commit(); 

sess = session.openSession();

//Person p1 = (Person)sess.load(Person.class,1L);
//System.out.println(p1.getPhone().getNumber());

// changed the above code to use the Criteria interface below: 
Criteria criteria = sess.createCriteria(Person.class);
List<Person> results = criteria.list();
for (int i=0; i<results.size(); i++){
  Person p = (Person)results.get(i);
  System.out.println(p.getPhone().getNumber());
}

Output:

Hibernate: 
    select
        phone_.id,
        phone_.number as number1_ 
    from
        phone phone_ 
    where
        phone_.id=?
Hibernate: 
    insert 
    into
        phone
        (number, id) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        person
        (name, phone_id, id) 
    values
        (?, ?, ?)
Hibernate: 
    select
        person0_.id as id0_1_,
        person0_.name as name0_1_,
        person0_.phone_id as phone3_0_1_,
        phone1_.id as id1_0_,
        phone1_.number as number1_0_ 
    from
        person person0_ 
    left outer join
        phone phone1_ 
            on person0_.phone_id=phone1_.id 
    where
        person0_.id=?
1234567

Ross 2010-05-28 21:08:45

Thanks for taking the time to test this out, Ross. I really appreciate it.. I've pasted in the full code of a smaller test. I'd be really interested if it work OK in your setup. It doesn't work in mine, even under 3.5.1-Final, but it may be something in my code, so I've pasted all of it.. Thanks :-)

Jeremy 2010-05-28 22:54:23

OK - we're on the track of this. If I do a load, as you do, I get the left outer join behavior. However, if I do list(), and then get the first object in the list, it does two selects - see my Edit Number 3 in the initial question

Jeremy 2010-05-28 23:08:29

Yes I am getting same results as you. Instead of using list try using iterate -- I gave that a try and seemed to work

Ross 2010-05-28 23:18:12

Thanks Ross. I'm not sure that iterate is a viable alternative: from the javadocs: "Entities returned as results are initialized on demand. The first SQL query returns identifiers only". That suggests that the 1+N scenario will still occur, just time-delayed when you go to use the objects, rather than when the initial call is made? As I understand it, list is not on-demand, but rather all in one go. I think the answer is just going to be a rather kludgy including of the joins in the HQL. Maybe it's better that it's explicit like this anyway..

Jeremy 2010-05-28 23:27:31

:-p, oh yes. Sorry you are right :-)

Ross 2010-05-28 23:33:20

I tried using the Criteria interface to get the list, instead of using hibernate query. It seemed to work. I will edit the above code for reference purposes.

Ross 2010-05-29 08:59:28

Answer 2

+2 A:

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.

I'm very interested by the code of the other answer because that's what I'm seeing too when testing the code you're showing, it generates two selects for a from Test2.

I'm using the following dependencies:

org.hibernate:hibernate-entitymanager:jar:3.4.0.GA:compile
org.hibernate:ejb3-persistence:jar:1.0.2.GA:compile
org.hibernate:hibernate-commons-annotations:jar:3.1.0.GA:compile
org.hibernate:hibernate-annotations:jar:3.4.0.GA:compile
org.hibernate:hibernate-core:jar:3.3.0.SP1:compile

I set the FetchType to EAGER out of desperation, even though it defaults to EAGER anyway for OneToOne mappings, but it made no difference.

This has no impact if you use Hibernate annotations because the Hibernate annotations overrides the EJB3 fetching options. See 2.4.5.1. Lazy options and fetching modes.

Pascal Thivent 2010-05-28 22:06:39

Thanks for taking the time, Pascal :-) That's good to get some replication. I've simplified the test case above. I guess either there's an error in my setup that someone will spot, or there is something funny in hibernate in this situation, though not in the one that Ross presents.

Jeremy 2010-05-28 22:56:24

I accepted your answer as correct, partly for testing out the problem (which Ross also did, and I'd mark his answer correct too if I could), but also because by replicating it, you prevented me from going insane :-)

Jeremy 2010-05-28 23:48:51

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