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I have two entities , Employee and publication : I want to show in a data table the publication title, date, and it's author stored in database : this is my query using JPQL :

private static EntityManager em;
private static EntityManagerFactory factory;

public PublicationDAO() {
    if(factory==null)
        factory=Persistence.createEntityManagerFactory("mavenTest");
    if(em==null)
        em=factory.createEntityManager();
}

public List<Object[]> getAllPublication() {
     em.getTransaction().begin();
     List<Object[]> pubs = em.createQuery("SELECT c.titrePublication, p.login FROM Publication c  JOIN c.employee p ").getResultList();
     em.getTransaction().commit();
     return pubs;
}

so I want to show this information in XHTML page's data table.

Omar · Answer 1 · 2018-09-13T20:52:55.060

I wonder why you make the type of the list "array of objects". Rendering it as type of your entity class is enough :

public List<Publication> getAllPublication() {
    ...
    List<Publication> pubs = ...
    ...
}

Specify a managedBean class in your presentation tier, to do the job :

@RequestScoped
@ManagedBean    
public class PublicationBean {

    // Inject your PublicationDAO here
    private PublicationDAO publicationDao;

    private List<Publication> publications;

    @PostConstruct 
    public retrievePublications () {
        try {
            publications = publicationDao.getAllPublication();
        } catch (Exception e) {
        }
    }

    public List<Publication> getPublications() {
        return this.publications;
    }
    public void setPublications(List<Publication> publications) {
        this.publications= publications;
    }

// getters/setters

}

Then, display the data with <h:dataTable> like this :

<h:dataTable value="#{publicationBean.publications}" var="p" rules="all">
    <h:column>
        <f:facet name="header">Publication title</f:facet>
        #{p.titrePublication}
    </h:column>
    <h:column>
        <f:facet name="header">Publication author</f:facet>
        #{p.employee.name}
    </h:column>
 </h:dataTable>

Don't populate the list in a constructor, do it in a `@Postconstruct` annotated method.https://stackoverflow.com/questions/5765853/how-and-when-should-i-load-the-model-from-database-for-hdatatable — Kukeltje, Sep 13 '18 at 06:45
Yeah, it was not good idea at that time.. I had preferred to use the least approach later. — Omar, Sep 13 '18 at 20:49

Shankari vatsalkumar · Answer 2 · 2014-05-21T07:34:43.620

Currently the query would return Array and what you need is a Construct return type..

create custom class (this will be your return type and it must have constructor which takes result values you define in query string. )

public class publicationModel

{

public String publicationName; public String author;
```
  public publicationModel (String publicationName, String author) 
  {
    this.publicationName= publicationName;
    this.author= author;
  } 
}
```
use typedQuery

String queryStr ="SELECT NEW example.publicationModel (c.titrePublication, p.login) " + "FROM Publication c JOIN c.employee p ";

TypedQuery query = em.createQuery(queryStr, publicationModel .class);

List <publicationModel> results = query.getResultList();

m not able to format the answer.. but i hope this helps..

score -1 · Accepted Answer · answered May 21 '14 at 21:52

hi finally I find the solution : the correct query should be :

List<Publication>=em.createQuery("select p from Publication p",Publication.Class).getResultList();

in the managed bean I should declare The author which is The Employee entity with getter and setter. then create a method called getAllpublications as :

public List<Publication> getAllpublications (){
publicationDao.getAllPublication();//this method is declared and specified in the DAO class
}

after that the xhtml page should look like:

<h:dataTable value="#{publicationBean.publications}" var="p" rules="all">
    <h:column>
        <f:facet name="header">Publication title</f:facet>
       <h:outputText value="#{p.titrePublication}"></h:outputText>
    </h:column>
    <h:column>
        <f:facet name="header">Publication author</f:facet>
        <h:outputText value="#{p.employee.name}"></h:outputText>
    </h:column>
 </h:dataTable>

so the solution is very close to your answer Omar thanks a lot for your help.

Bad practice to call the dao non-lazy in the getter of the publications. You'll call the dao waaay to many times then. https://stackoverflow.com/questions/2090033/why-jsf-calls-getters-multiple-times, https://stackoverflow.com/questions/5765853/how-and-when-should-i-load-the-model-from-database-for-hdatatable — Kukeltje, Sep 13 '18 at 06:44

3 Answers3