java - Hibernate:复合 id 服务

Question

我的实体:文章、类别。这是一种 n:m 关系。我想获取特定类别引用的文章数量。

这是我的实体:

@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 );
    }
}

现在我有了文章和类别的存储库和服务层。我只会提供文章层来显示结构。

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 );
    }
}

如何根据类别获取文章的大小？我是否需要为 ArticleCategory 创建另一个存储库/服务层对？它应该是什么样子，因为我得到:

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

你的异常与你的问题和Hibernate无关，结束与Spring有关的一切。 Spring 找不到任何 ArticleCategoryDAO 类型的 Spring bean。您可能忘记用 @Repository 对其进行注释。

顺便说一句，您询问是否应该为 ArticleCategory 创建一个 DAO，但错误消息显示您已经创建了一个。

附带问题:为什么不在 Article 和 Category 之间简单地创建一个 ManyToMany 关联？根本不需要 ArticleCategory 实体。