CODEWITHSUNDEEP
springjpalazy-loading
robert trudel
robert trudel

Reputation: 5749

lazy loading return null value

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?

Upvotes: 1

Views: 4849

Answers (3)

user980089
user980089

Reputation: 374

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.

Upvotes: 0

zagyi
zagyi

Reputation: 17518

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);
    }
}

Upvotes: 4

Atropo
Atropo

Reputation: 12531

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

Upvotes: 1

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