lazy loading return null value

Question

i use spring 3.2, spring data and jpa.

i save an Advertisement object, after i save message

i try to access message from Advertisement but it's null

@Entity
public class Advertisement implements Serializable {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;

@OneToMany(mappedBy="id", cascade={CascadeType.REMOVE}, fetch=FetchType.LAZY)
private Set<Message> messages;
}

@Entity
public class Message implements Serializable {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;

@ManyToOne
private Advertisement advertisement;
}

test unit

Advertisement ads = new Advertisement();
ads = advertisementRepo.save(ads);

assertNotNull(ads);
assertNotNull(ads.getId());

Message message = new Message();
message.setAdvertisement(ads);
message = msgRepo.save(message);

ads = advertisementRepo.findOne(ads.getId());
ads.getMessages(); //return null

why ads.getMessages() don't return messages?

zagyi · Accepted Answer · 2013-07-24 16:58:05Z

4

The problem is that bidirectional relationships are not transparently managed by JPA. When manipulating one side of a bidirectional relationship, the application has to ensure that the other side is updated accordingly.

This can easily be done by writing setter methods that update the associated entity as well. For example, when setting the Advertisment of a Message, you can add the Message instance to the collection in Advertisment:

@Entity
public class Message implements Serializable {

    ...

    public void setAdvertisement(Advertisement advertisement) {
        this.advertisement = advertisement;
        advertisement.getMessages().add(this);
    }
}

edited Jul 24, 2013 at 16:58

answered Jul 24, 2013 at 16:52

zagyi

17.6k4 gold badges54 silver badges50 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

robert trudel Over a year ago

that work but in Advertisement, i need to do: Set<Message> messages = new HashSet<Message>(); before i had: Set<Message> messages;

zagyi Over a year ago

Sure, you need to initialize the collection, I forgot to mention that.

Atropo · Accepted Answer · 2013-07-24 16:52:58Z

1

Try to save the Advertisement after you assign it a new Message collection:

Advertisement ads = new Advertisement();
ads = advertisementRepo.save(ads);

assertNotNull(ads);
assertNotNull(ads.getId());

Message message = new Message();
message.setAdvertisement(ads);
ads.setMessages(new HashSet<Message>());
ads.getMessages().add(message);
ads = advertisementRepo.save(ads);
message = msgRepo.save(message);

ads = advertisementRepo.findOne(ads.getId());
ads.getMessages(); //return null

edited Jul 24, 2013 at 16:52

answered Jul 24, 2013 at 16:47

Atropo

12.6k8 gold badges51 silver badges62 bronze badges

Comments

user980089 · Accepted Answer · 2013-07-24 16:58:16Z

0

This is returning null because you are saving the non-owning entity first and then the owning entity. If you save message before ads it should return non-null value.

answered Jul 24, 2013 at 16:58

user980089

3741 gold badge3 silver badges11 bronze badges

Collectives™ on Stack Overflow

lazy loading return null value

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related