我的实体:文章,类别。这是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。
我将仅提供“文章”层以显示结构。
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 );
}
}
如何获得基于类别的文章大小?我是否需要为ArticleCategory创建另一个存储库/服务层对?看起来如何,因为然后我得到:
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: {}
最佳答案
您的异常与您的问题无关,并且休眠,结束与Spring有关的一切。 Spring找不到任何ArticleCategoryDAO
类型的Spring bean。您可能忘记了使用@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:为什么不简单地在Article和Category之间创建ManyToMany关联?完全不需要ArticleCategory
实体。