update while doing save in hibernate

[Naresh Chaurasia]

I am trying to perform save operation in hibernate3.

I have the following java class

  public class Location {

    private Long id;
    private String name;
    private String address;
}  

The corresponding config file

<hibernate-mapping package="com.entity.association">
<class name="Location" table="ora_locations">
<id name="id" type="long">
<generator class="native"/>
</id>
<property name="name" type="string"/>
<property name="address" type="string"/>
</class>
</hibernate-mapping>

Code for saving the object

Location l = new Location();
l.setName("name");
session.save(l);

When i execute the above code, i get the following output in sql.

 Hibernate: insert into GC820NODE3.ora_locations (name, address, id) values (?, ?, ?)
Hibernate: update GC820NODE3.ora_locations set name=?, address=? where id=?
   

I wanted to understand that what is the need for first doing insert and then performing update. I re-executed the code with using the assigned generator, but i get the same SQLs.

Thanks in advance.

[Paul Sturrock]

Its doing an insert because your location does not have an id.

[Naresh Chaurasia]

All of this(insert and update) could have been done in single operation(insert), instead of first doing insert and then update. What is the advantage of performing 2 operations.

[Paul Sturrock]

None. Are you sure this is the only operation you perform against this object in the current transaction?

[Naresh Chaurasia]

Ok. I did some more coding to understand the concept and found the following

This are my Event, Attendee, Location,Speaker classes.

   
public class Event {
private Long id;
private String name;
private Date startDate;
private int duration;
private Set speakers;
private Set attendees;
private Location location;
}

public class Attendee {
private Long id;
private String firstName;
private String lastName;
}


public class Speaker {
private Long id;
private String firstName;
private String lastName;
}


public class Location {
private Long id;
private String name;
private String address;
}       
        

These are my config files.

Event.hbm.xml

<hibernate-mapping package="com.manning.hq.ch03">
    <class name="Event" table="events">
        <id name="id" type="long" unsaved-value="null">
            <generator class="native"/>
        </id>
        <property name="name" type="string" length="100"/>
        <property name="startDate" column="start_date"
                  type="date"/>
        <property name="duration" type="integer"/>
        <many-to-one name="location" column="location_id"
                     class="Location"/>
        <set name="speakers" cascade="all">
            <key column="event_id"/>
            <one-to-many class="Speaker"/>
        </set>
        <set name="attendees" cascade="all">
            <key column="event_id"/>
            <one-to-many class="Attendee"/>
        </set>
    </class>
</hibernate-mapping>

Now if i try to do the following

Case1: Instantiating only Event and not associated object(Attendees, Speaker)

Event event = new Event();
e.setName("testSave");
session.saveOrUpdate(event);

i get the following output sql.

insert into GC820NODE3.events (name, start_date, duration, location_id, id) values (?, ?, ?, ?, ?)

But if i perform the following operation

Case2: Instantiating Event and associated object(Attendees, Speaker) as shown below

e.setName("testSaveWithCascades");

e.setSpeakers(new HashSet());
e.getSpeakers().add(new Speaker("John", "Doe"));
e.getSpeakers().add(new Speaker("Jane", "Doe"));

e.setAttendees(new HashSet());
e.getAttendees().add(new Attendee("John", "Smith"));
e.getAttendees().add(new Attendee("Jane", "Smith"));

Long id = manager.save(e);

i get the following output sql.

Hibernate: insert into GC820NODE3.events (name, start_date, duration, location_id, id) values (?, ?, ?, ?, ?)
Hibernate: insert into GC820NODE3.speakers (firstName, lastName, id) values (?, ?, ?)
Hibernate: insert into GC820NODE3.speakers (firstName, lastName, id) values (?, ?, ?)
Hibernate: insert into GC820NODE3.attendees (firstName, lastName, id) values (?, ?, ?)
Hibernate: insert into GC820NODE3.attendees (firstName, lastName, id) values (?, ?, ?)
Hibernate: update GC820NODE3.speakers set event_id=? where id=?
Hibernate: update GC820NODE3.speakers set event_id=? where id=?
Hibernate: update GC820NODE3.attendees set event_id=? where id=?
Hibernate: update GC820NODE3.attendees set event_id=? where id=?

Conclusion:

Does that mean that when i save only Event(Case1), only inserts is done.
If i save Event, which has associated speaker and attenedes(Case2)
first Event is inserted, then the speakers and attendes are inserted and finally the event_id are set in speakers and attendees.

Why does hibernate perform inserts and update, when the entire operation could have been done using inserts. Is there any advantage of doing so?

[Arun Kumarr]

Can you post your table structure?

[Naresh Chaurasia]

I am using the following tables, constraints and views while executing the above program.

      create table GC820NODE3.attendees (
        id number(19,0) not null,
        firstName varchar2(20),
        lastName varchar2(20),
        event_id number(19,0),
        primary key (id)
    );

    create table GC820NtintgODE3.events (
        id number(19,0) not null,
        name varchar2(100),
        start_date date,
        duration number(10,0),
        location_id number(19,0),
        primary key (id)
    );

    create table GC820NODE3.locations (
        id number(19,0) not null,
        name varchar2(255),
        address varchar2(255),
        primary key (id)
    );

    create table GC820NODE3.speakers (
        id number(19,0) not null,
        firstName varchar2(20),
        lastName varchar2(20),
        event_id number(19,0),
        primary key (id)
    );

    alter table GC820NODE3.attendees 
        add constraint FKEADFCAF9470CF8C 
        foreign key (event_id) 
        references GC820NODE3.events;

    alter table GC820NODE3.events 
        add constraint FKB307E1192B576C48 
        foreign key (location_id) 
        references GC820NODE3.locations;

    alter table GC820NODE3.speakers 
        add constraint FK80C3A054470CF8C 
        foreign key (event_id) 
        references GC820NODE3.events;

    create sequence GC820NODE3.hibernate_sequence; 

[Arun Kumarr]

Can you try adding ownership at the events hbm file by specifying,

<set name="speakers" inverse="true">

[Naresh Chaurasia]

If i add the above line i get the expected output

 
Hibernate: insert into GC820NODE3.events (name, start_date, duration, location_id, id) values (?, ?, ?, ?, ?)
Hibernate: insert into GC820NODE3.speakers (firstName, lastName, id) values (?, ?, ?)
Hibernate: insert into GC820NODE3.speakers (firstName, lastName, id) values (?, ?, ?)
Hibernate: insert into GC820NODE3.attendees (firstName, lastName, id) values (?, ?, ?)
Hibernate: insert into GC820NODE3.attendees (firstName, lastName, id) values (?, ?, ?)
   

Can you please explain why it is so?

[Arun Kumarr]

As I said, it displays ownership of the items and it reflects on cascade of saves. More on hibernate documentation.