[FIXED] JPA annotation with association table

Issue

I'm using JPA annotation with Hibernate and I don't really know how to manage an association table.

The entity relationship

Here is my database schema as entity-relationship (ER) diagram:

  COUNTRY          COUNTRY_MOVIE        
|---------|*    *|---------------|      | MOVIE   |
| COU_ID  |<---->| COUNTRY_ID    |*    *|---------|
| LABEL   |      | MOVIE_ID      |<---->| MO_ID   |
|---------|      |---------------|      | LABEL   |
                                        |---------|

The table COUNTRY_MOVIE is an association table between COUNTRY and MOVIE with many-to-many associations (symbolized by the arrow-lines above where many-to-many expressed by * *) .

The entities modeled in code with JPA

In my JPA object I didn't create a CountryMovie.java class.

Country

But I use @JoinTable in Country.java as in the following code:

//Package, Import...

@Entity
@Table(name="COUNTRY")
public class Country implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="COU_ID")
    private Integer couID;

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

    //bi-directional many-to-many association to TFilmFil
    @ManyToMany
    @JoinTable(
        name="COUNTRY_MOVIE"
        , joinColumns={
            @JoinColumn(name="COU_ID")
            }
        , inverseJoinColumns={
            @JoinColumn(name="MO_ID")
            }
        )
    private List<Movie> movies;

    public Country() {
        super();
    }
    
    // Other constructor, Getter & Setter, and "toString" method...
}

Movie

And in Movie.java I use only a @ManyToMany annotation :

//Package, Import...

@Entity
@Table(name="MOVIE")
public class Movie implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="MO_ID")
    private Integer moId;

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

    //bi-directional many-to-many association to TrPaysPay
    @ManyToMany(mappedBy="movies")
    private List<Country> countries;

    public Film() {
        super();
    }

    // Other constructor, Getter & Setter, and "toString" method...
}

---

Issue 1: LazyInitializationException

I don't know if it's the best way to manage this kind of association table even if it looks OK.

But when I try to get all the countries of a movie I obtain a LazyInitializationException from Hibernate.

Issue 2: After I tried FetchType.EAGER

So I tried to add a fetch EAGER to each many-to-many annotation:

In Country:

@ManyToMany(fetch=FetchType.EAGER)
@JoinTable(

In Movie:

@ManyToMany(mappedBy="movies",fetch=FetchType.EAGER)

Then I obtain this :

org.springframework.beans.factory.support.DefaultSingletonBeanRegistry destroySingletons

Questions

1. Do I have to create another java class to map COUNTRY_MOVIE?
2. Or is there a way to fix this problem by using the same java class as now?

Solution

Your mapping is alright (you don't need a third class). You also don't need to make it eager fetch. The problem is with the querying code. You should make sure that the session is still open when you access the collection.

Update the question with your query code and I can tell you how to fix it.

Answered By - gkamal