Inserting into table with Hibernate question

[Henrik Engert]

Hi,

I am creating a small application for myself and I am trying to insert a Radio object into the database through the Pilot Object. It is a one-to-one relationship. It seems to insert the data, since I can list the pilots and their radios after insert. But if I run the app again the pilots don't have any Radios, they are NULL. I use PilotDAO to insert data like this:

 
   Radio radio = new Radio("Futaba 14MZ", "64");
   Pilot pilot = pilotDao.create("Henrik", "Engert", radio);

I use Derby database. The pilots stick to the tables but not the radios.

I have the following:

POJO's:

Person:

public class Person {
    private String firstname;
    private String lastname;
 
 
    public Person() {
    }
 
    public Person(String firstname, String lastname) {
        this.firstname = firstname;
        this.lastname = lastname;
    }
 
    public String getFirstname() {
        return firstname;
    }
 
    public void setFirstname(String firstname) {
        this.firstname = firstname;
    }
 
    public String getLastname() {
        return lastname;
    }
 
    public void setLastname(String lastname) {
        this.lastname = lastname;
    }
}

Pilot:

public class Pilot extends Person implements Serializable {
    private long id;
    private Radio radio;
 
 
    public Pilot() {
    }
 
    public Pilot(String firstname, String lastname) {
        super(firstname, lastname);
    }
 
    public Pilot(String firstname, String lastname, Radio radio) {
        super(firstname, lastname);
        this.radio = radio;
    }
 
    public Radio getRadio() {
        return radio;
    }
 
    public void setRadio(Radio radio) {
        this.radio = radio;
    }
 
    public long getId() {
        return id;
    }
 
    public void setId(long id) {
        this.id = id;
    }
 
 
    public String toString() {
        return id + " " + getFirstname() + " " + getLastname() + getRadio();
    }
}

Radio:

public class Radio implements Serializable {
    private long id;
    private String name;
    private String freq;
 
 
    public Radio() {
    }
 
    public Radio(String name, String freq) {
        this.name = name;
        this.freq = freq;
    }
 
    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 String getFreq() {
        return freq;
    }
 
    public void setFreq(String freq) {
        this.freq = freq;
    }
 
 
    public String toString() {
        return "Radio " + name;    //TODO
    }
}

Hibernate mapping:

<?xml version="1.0" encoding="utf-8"?>
        <!DOCTYPE hibernate-mapping
                PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
                "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="model.Pilot" table="PILOT">
        <id name="id" type="long" column="id">
            <generator class="native"/>
        </id>
 
        <property name="firstname" column="firstname" type="string"/>
 
        <property name="lastname" column="lastname" type="string"/>
 
        <one-to-one name="radio" class="model.Radio" constrained="false"/>
        
    </class>
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8"?>
        <!DOCTYPE hibernate-mapping
                PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
                "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="model.Radio" table="Radio">
        <id name="id" type="long" column="id">
            <generator class="native"/>
        </id>
 
        <property name="name" column="name" type="string"/>
 
        <property name="freq" column="freq" type="string"/>
 
    </class>
</hibernate-mapping>

public class PilotDAO extends DAO {
 
    public PilotDAO()  {
    }
 
    public Pilot create(String firstName, String lastName) throws PilotException {
        try {
            begin();
            Pilot pilot = new Pilot(firstName, lastName);
            getSession().save(pilot);
            commit();
            return pilot;
        } catch (HibernateException e) {
            rollback();
            throw new PilotException(e.getMessage());
        }
    }
 
    public Pilot create(String firstName, String lastName, Radio radio) throws PilotException {
        try {
            begin();
            Pilot pilot = new Pilot(firstName, lastName, radio);
            getSession().save(pilot);
            commit();
            return pilot;
        } catch (HibernateException e) {
            rollback();
            throw new PilotException(e.getMessage());
        }
    }
 
    public Pilot getPilot(long id) throws PilotException {
        try {
            begin();
            Query q = getSession().createQuery("from Pilot where id = :id");
            q.setLong("id", id);
            Pilot pilot = (Pilot)q.uniqueResult();
            commit();
            return pilot;
        } catch (HibernateException e) {
            rollback();
            throw new PilotException(e.getMessage());
        }
    }
 
    public List getAllPilots() throws PilotException {
        try {
            begin();
            Query q = getSession().createQuery("from Pilot");
            List list = q.list();
            commit();
            return list;
        } catch (HibernateException e) {
            rollback();
            throw new PilotException(e.getMessage());
        }
    }
}

[ February 14, 2007: Message edited by: Henrik Engert ]

[sathish kumar]

Do you think if the sessions are being handled properly? That might be an issue for you to think about. Looking at your code, looks well to me.

[Henrik Engert]

I have based my code from the "Beginning Hibernate (Apress)" book.

If one object contains another object (one-to-one relationship) should Hibernate handle the inserts into both tables?

[Mark Spritzler]

"skumar"

You have been warned before, plese change your display name to meet the JavaRanch Naming Policy of using your real first and real last names or you account will be suspended.

Thanks

Mark

[Mark Spritzler]

You are missing cascade options to tell Hibernate what to do with the related objects.

Try this

Change
<one-to-one name="radio" class="model.Radio" constrained="false"/>

to

<one-to-one name="radio" class="model.Radio" constrained="false" cascade="save-update"/>

Mark

[Henrik Engert]

That worked a little bit better. It actually inserted the values correctly.

But now I can't select the Pilots radio.

I thought it would handle the following call for me:

Query q = getSession().createQuery("from Pilot");
      List list = q.list();

When I look at the tables in DBVisualizer I don't see any connection between the Pilto table and the Radio table. No id refers to the Radio table at all.

The pilot mapping xml now has the following line of code:

<one-to-one name="radio" class="model.Radio" constrained="false" cascade="save-update"/>

and the Radio mapping xml now has the following line of code:

<one-to-one name="pilot" class="model.Pilot" constrained="false"/>

Any ideas?

Thanks.

[Mark Spritzler]

In a one-to-one mapping, Hibernate can use a couple of approaches for PK/FK relationships. You see in a database, in terms of referential integrity, does not have a concept of one-to-one. You can either have the two tables share the same PK value, which is what I believe is in your schema. Or you could have one table have a FK value to a PK in the other table.

So in your case it looks like the PK of both tables are the same. So the Radio that corresponds to the Pilot record would have the same PK value. That is what the "constrained=true" does.

Now, the next thing about the Query, and your new mapping. So now you are mapping a bi-directional mapping, which means your Radio needs to have a reference to the Pilot.

Your Pilot query returns a Pilot, but there is no Radio put in it until you try to access the radio via, getRadio() method. This is called lazy loading. Hibernate will not load the Radio in the first query because it is by default lazy loaded. So you can add to your

<one-to-one name="radio" class="model.Radio" constrained="false" cascade="save-update"/>

add

  lazy="false" fetch="join"  

setting to lazy="false" means it will eager fetch the Radio at the point of your query to Pilot. However, it will still be two SQL statements to the database. To make it just one SQL statement the fetch="join" will make it run in one query using a LEFT OUTER JOIN.

Good Luck.

Mark