failed to lazily initialize a collection and vaadin

Hello I have a problem with vaadin and lazy load of my entity
my entity contains a rellationship one-to-many and many-to-one with this way

@Entity
@Table(name = "Categories")
public class Category extends AbstractEntity {
private static final long serialVersionUID = 1L;

private String name;
@ManyToOne
@JoinColumn(name = "parent")
private Category parent;
@Column
@OneToMany(mappedBy = "parent", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
private List<Category> children = new ArrayList<>();

public Category()


so i have this controller

@Transactional
public class CategoryService{

@PersistenceContext
private EntityManager em;


public void save(Category category)
..



public Collection<Category> all()
return em
.createQuery("select category from Category category",Category.class)
.getResultList();




when i try to load and print for each entity her children it was successfull but it was on setup.When i use my form in vaadin and i call service.all()
and try to do the same thing i have the

org.hibernate.LazyInitializationException: failed to lazily
initialize a collection of role: models.Category.children, could not
initialize proxy - no Session

Service:

@Inject
public CategoriesView(CategoryService service)
this.service = service;
list= (List<Category>) service.all();


@Override
protected Component initContent()
HorizontalLayout layout = new HorizontalLayout();
for (Category cate : list)
System.out.println(cate.getChildren());




What can i do to have wanted result?

1 Answer
1

i solved my problem by this way
i initialized my data-providers in my enter method and i did this

@Override
public void enter(ViewChangeListener.ViewChangeEvent event)
parents = DataProvider.ofCollection(service.all());
parentGrid.setDataProvider(parents);




edit also i put my selectionListener into the enter method

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