LazyInitializationException after return updated entity

Question

I have some model with two relations:

@Entity
@Table(name = "data_model")
public class DataModel {

    @Id
    @GeneratedValue
    @Column(name = "model_id")
    private Integer id;

    @Column(name = "name")
    private String name;

    @OneToMany(mappedBy = "dataModel", cascade = {CascadeType.PERSIST, CascadeType.REMOVE, CascadeType.MERGE})
    private List<OutputField> outputFields;

    @OneToMany(mappedBy = "dataModel", cascade = {CascadeType.PERSIST, CascadeType.REMOVE, CascadeType.MERGE})
    private List<Query> queries;

    //some another fields
}

I use Spring Data JPA and I want to update entity. I write simple service:

@Service
public class DataModelService {

    @Autowired
    private DataModelRepository dataModelRepository;

    @Transactional
    public DataModel createOrUpdate(DataModel dataModel) {
       return dataModelRepository.save(dataModel);
    }

    //another methods
}

I write simple test:

public class DataModelServiceTest {
    @Autowired
    private DataModelService dataModelService;

    @Test
    void shouldUpdateDataModel() {
       DataModel dataModelBeforeUpdate = dataModelService.getById(1);
       dataModelBeforeUpdate.getQueries().get(0).setSqlQuery("SELECT 1");
       DataModel updatedModel = dataModelService.createOrUpdate(dataModelBeforeUpdate);
       assertThat(updatedModel.getQueries(), notNullValue());
    }
}

But, I get error, when I try to call method getQieries() :

Unable to evaluate the expression Method threw 'org.hibernate.LazyInitializationException' exception.

In debug I see:

Questions:

1. Why does this error occur and how can I fix it? How do I make hibernate return all links after an update?
2. Why is the outputFields field filled in correctly, but the queries field is not?

Answer 1

It happens because you are trying to initialize collection outside a transaction. To fix this add @DataJpaTest and @RunWith(SpringRunner.class) annotations to your test class. By default, data JPA tests are transactional.

Refer here for more details.