跳至主要内容

JPA 2.1: Treat


JPA 2.1: Treat

JPA 2.1 introduces a new keyword treat in JPQL which allow path expressions to be treated as a subclass, giving access to subclass specific state.
Create two specified Comments, VoteUp and VoteDown.
@Entity
public class VoteUp  extends Comment{

    public VoteUp() {
        super("Up");
    }
    
}

@Entity
public class VoteDown  extends Comment{

    public VoteDown() {
        super("Down");
    }
    
}
Add an @Inheritance annotation on Comment entity.
@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public class Comment implements Serializable {
}
In the ViewPostBean, fetch the counts of voteUp comments and voteDown comments.
private void fetchVoteDown() {
 this.voteDown = ((Long) (em.createQuery("select count(vu)from Post p join treat(p.comments  as VoteDown) vu where p.id=:id")
  .setParameter("id", this.id)
  .getSingleResult())).intValue();
}

private void fetchVoteUp() {
 this.voteUp = ((Long) (em.createQuery("select count(vu)from Post p join treat(p.comments  as VoteUp) vu where p.id=:id")
  .setParameter("id", this.id)
  .getSingleResult())).intValue();
}
Also create a voteUp() and voteDown() methods to create VoteUp and VoteDown objects.
public void voteUp() {
 final VoteUp comment = new VoteUp();
 comment.setPost(this.post);
 this.post.getComments().add(comment);

 em.merge(this.post);
 em.flush();

 fetchVoteUp();
}

public void voteDown() {
 final VoteDown comment = new VoteDown();
 comment.setPost(this.post);
 this.post.getComments().add(comment);

 em.merge(this.post);
 em.flush();

 fetchVoteDown();
}
The sample codes are hosted on my github.com account, check out and play it yourself.
标签：

评论

发表评论

此博客中的热门博文

Create a restful application with AngularJS and Zend 2 framework

Create a restful application with AngularJS and Zend 2 framework This example application uses AngularJS/Bootstrap as frontend and Zend2 Framework as REST API producer. The backend code This backend code reuses the database scheme and codes of the official Zend Tutorial, and REST API support is also from the Zend community. Getting Started with Zend Framework 2 Getting Started with REST and Zend Framework 2 Zend2 provides a   AbstractRestfulController   for RESR API producing. class AlbumController extends AbstractRestfulController { public function getList() { $results = $this->getAlbumTable()->fetchAll(); $data = array(); foreach ($results as $result) { $data[] = $result; } return new JsonModel(array( 'data' => $data) ); } public function get($id) { $album = $this->getAlbumTable()->getAlbum($id); return new JsonModel(array("data" =...
发表评论
阅读全文

JPA 2.1: Attribute Converter

JPA 2.1: Attribute Converter If you are using Hibernate, and want a customized type is supported in your Entity class, you could have to write a custom Hibernate Type. JPA 2.1 brings a new feature named attribute converter, which can help you convert your custom class type to JPA supported type. Create an Entity Reuse the   Post   entity class as example. @Entity @Table(name="POSTS") public class Post implements Serializable { private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy = GenerationType.AUTO) @Column(name="ID") private Long id; @Column(name="TITLE") private String title; @Column(name="BODY") private String body; @Temporal(javax.persistence.TemporalType.DATE) @Column(name="CREATED") private Date created; @Column(name="TAGS") private List<String> tags=new ArrayList<>(); } Create an attribute convert...
发表评论
阅读全文

Auditing with Hibernate Envers

Auditing with Hibernate Envers The approaches provided in JPA lifecyle hook and Spring Data auditing only track the creation and last modification info of an Entity, but all the modification history are not tracked. Hibernate Envers fills the blank table. Since Hibernate 3.5, Envers is part of Hibernate core project. Configuration Configure Hibernate Envers in your project is very simple, just need to add   hibernate-envers   as project dependency. <dependency> <groupId>org.hibernate</groupId> <artifactId>hibernate-envers</artifactId> </dependency> Done. No need extra Event listeners configuration as the early version. Basic Usage Hibernate Envers provides a simple   @Audited   annotation, you can place it on an Entity class or property of an Entity. @Audited private String description; If   @Audited   annotation is placed on a property, this property can be tracked. @Entity @Audited public clas...
1 条评论
阅读全文