Question

I got relations many to many between restaurant and tag. Here are my classes:

public class Restaurant {
    @Id
    @GeneratedValue
    private int id;
(...)
    @ManyToMany
    @JoinTable(name="restaurant_tag",
            joinColumns={@JoinColumn(name="restaurant_id")},
            inverseJoinColumns={@JoinColumn(name="tag_id")})
    private List<Tag> tags;

and:

public class Tag {
    @Id
    private int id;
    private String name;
    @ManyToMany
    @JoinTable(name="restaurant_tag",
            joinColumns={@JoinColumn(name="tag_id")},
            inverseJoinColumns={@JoinColumn(name="restaurant_id")})
    private List<Restaurant> restaurants;

I want to displays all the tags connected with my restaurant. Here’s controller:

modelMap.addAttribute("tagList", restaurant.getTags());

In my jsp:

<c:forEach items="${tagList }" var="var"><c:out value="${var }" ></c:out></c:forEach>

When i go to the restaurant page, i got error:

org.hibernate.LazyInitializationException:
failed to lazily initialize a
collection of role:
beans.Restaurant.tags, no session or
session was closed

Answer 1

This happens because your DAO closes the hibernate session before the collection can be fetched.

Have a look at the “Open Session In View” pattern, this is the most common solution to this problem.