Hibernate: Composite-id Service

Question

My Entities: Article, Category. It's an n:m relationship. I would like to get the number of Articles referenced with a specific Category.

Here are my entities:

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

    @Id
    @Column( nullable = false )
    @GeneratedValue( strategy = GenerationType.IDENTITY )
    private Integer id;

    @Column( nullable = false )
    private String title;

    @Column( nullable = false )
    private Date creationDate = new Date();

    @Lob
    @Type( type = "org.hibernate.type.StringClobType" )
    @Column( nullable = false )
    private String text;

    // Getter + setter
}

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

    @Id
    @Column( nullable = false )
    @GeneratedValue( strategy = GenerationType.IDENTITY )
    private Integer id;

    @Column( nullable = false )
    private String title;

    // Getter + setter
}

@Entity
@Table( name = "tbl_articles_categories" )
@AssociationOverrides({
    @AssociationOverride( name = "pk.article", joinColumns = @JoinColumn( name = "article_id" ) ),
    @AssociationOverride( name = "pk.category", joinColumns = @JoinColumn( name = "category_id" ) )
})
public class ArticleCategory
{
    @EmbeddedId
    private ArticleCategoryPK pk = new ArticleCategoryPK();

    public ArticleCategoryPK getPk() ...

    public void setPk( ArticleCategoryPK pk ) ...

    @Transient
    public Article getArticle()
    {
        return pk.getArticle();
    }

    public void setArticle( Article article )
    {
        pk.setArticle( article );
    }

    @Transient
    public Category getCategory()
    {
        return pk.getCategory();
    }

    public void setCategory( Category category )
    {
        pk.setCategory( category );
    }
}

Now I have the repository and service layers for Article and Category. I will only provide the Article layers to show the structure.

public abstract class BaseDAO<E>
{
    public abstract List<E> list( int offset, int limit );
    public abstract void delete( int id );
    public abstract void save( E entity );
    public abstract E get( int id );
    public abstract List<E> list();
    public abstract Integer size();
}

@Repository
public class ArticleDAO extends BaseDAO<Article>
{
    @Autowired
    private SessionFactory sessionFactory;

    @Override
    public void delete( int id )
    {
        Article article = get( id );

        if ( article != null )
        {
            sessionFactory.getCurrentSession().delete( article );
        }
    }

    @Override
    public void save( Article article )
    {
        sessionFactory.getCurrentSession().save( article );
    }

    @Override
    public Article get( int id )
    {
        return ( Article ) sessionFactory.getCurrentSession().load( Article.class, id );
    }

    @SuppressWarnings( "unchecked" ) // The type is determined by the HQL query but the interface returns an untyped list
    @Override
    public List<Article> list()
    {
        return sessionFactory.getCurrentSession().createQuery( "from Article" ).list();
    }

    @Override
    public Integer size()
    {
        Number ret = ( Number ) criteria.setProjection( Projections.rowCount() ).uniqueResult();
        return ret.intValue();
    }
}

public abstract class BaseService<E, D extends BaseDAO<E>>
{
    protected D dao;

    public BaseService()
    {
    }

    protected D getDao()
    {
        return dao;
    }

    @Autowired
    protected void setDAO( D dao )
    {
        this.dao = dao;
    }

    @Transactional
    public void delete( int id )
    {
        dao.delete( id );
    }

    @Transactional
    public void save( E entity )
    {
        dao.save( entity );
    }

    @Transactional
    public E get( int id )
    {
        return dao.get( id );
    }

    @Transactional
    public List<E> list()
    {
        return dao.list();
    }

    @Transactional
    public Integer size()
    {
        return dao.size();
    }
}

@Service
public class ArticleService extends BaseService<Article, ArticleDAO>
{
    public ArticleService()
    {
        setDAO( dao );
    }
}

How can I get the size of Articles based on a Category? Do I need to create another Repository/Service layer pair for ArticleCategory? How should it look like because then I'm getting:

No matching bean of type [com.example.model.ArticleCategoryDAO] found for
dependency: expected at least 1 bean which qualifies as autowire candidate for
this dependency. Dependency annotations: {}

Answer 1

Your exception has nothing to do with your question and Hibernate, end everything to do with Spring. Spring doesn't find any Spring bean of type ArticleCategoryDAO . Your probably forgot to annotated it with @Repository .

BTW, you ask if you should create a DAO for ArticleCategory , but the error message shows that you have created one already.

Side question: why not simply create a ManyToMany association between Article and Category? The ArticleCategory entity isn't needed at all.