Question

I am trying to implement lazy loading within my primefaces datatable setup. Currently, this is working without the lazy loading implementation, but I get no data in the datatable after implementing the lazy loading. However, I can print my list within my LoadData method to verify that the data is getting loaded into my list, but there seems to be an issue once my LazyModel is returned and the datatable loading is attempted. This could just be something simple that I’m overlooking. Any help is greatly appreciated!

Here is my ScreenshotListProducer class code:

    @ManagedBean
    @RequestScoped
    public class ScreenshotListProducer implements Serializable  {
       private static final long serialVersionUID = 1L;
       @Inject
       private EntityManager em;

       private List<Screenshot> screenshots;

       private LazyDataModel<Screenshot> lazyModel = null;

       private int pageSize = 5;

       public void setPageSize(int pageSize) {
           this.pageSize = pageSize;
       }

       public int getPageSize() {
           return pageSize;
       }

       @Produces
       @Named
       public List<Screenshot> getScreenshots() {
          System.out.println("************* getting screenshots list **************");
          return screenshots;
       }

       @PostConstruct
       public void LoadData() {
            lazyModel = new LazyDataModel<Screenshot>() {
                private static final long serialVersionUID = 1L;

                    @Override
                    public List<Screenshot> load(int first, int pageSize, String sortField, SortOrder sortOrder, Map<String,String> filters) {      
                    int start = first;
                    int end = first + pageSize;

                    try {
                        CriteriaBuilder cb = em.getCriteriaBuilder();
                        CriteriaQuery<Screenshot> criteria = cb.createQuery(Screenshot.class);
                        Root<Screenshot> screenshot = criteria.from(Screenshot.class);
                        criteria.select(screenshot).orderBy(cb.asc(screenshot.get("time")));

                        TypedQuery<Screenshot> s = em.createQuery(criteria);
                        s.setMaxResults(end - start);
                        s.setFirstResult(start);

                        screenshots = s.getResultList();
                        System.out.println("************* lazy screenshot list created **************");
                        for (Screenshot lazylist : screenshots) {
                          System.out.println("id numbers in lazy list: " + lazylist.getId());
                        }
                    } catch (NullPointerException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }

                    return screenshots;
                  }
            };
       }

   public LazyDataModel<Screenshot> getLazyModel() {
        return lazyModel;
    }

Here is my Screenshot class:

@Entity
@XmlRootElement
@Table(name="Test2012", uniqueConstraints = @UniqueConstraint(columnNames = "id"))
public class Screenshot implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue
    @Column(name = "id", columnDefinition="INT")
    private Long id;

    private Timestamp time;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Timestamp getTime() {
        return time;
    }

    public void setTime(Timestamp time) {
        this.time = time;
    }   
}

Here is my xhtml code:

    <p:dataTable id="table1" var="scrshot" rowKey="#{scrshot.id}" value="#{screenshotListProducer.lazyModel}" paginator="true" rows="7" paginatorPosition="bottom" 
                 paginatorTemplate="{CurrentPageReport}  {FirstPageLink} {PreviousPageLink} {PageLinks} {NextPageLink} {LastPageLink} {RowsPerPageDropdown}"  
                 rowsPerPageTemplate="7,20,50,100" widgetVar="dataTable" currentPageReportTemplate="(Number of Records: {totalRecords})"
                 emptyMessage="No screenshot data found with given criteria" lazy="true" scrollable="true" draggableColumns="true" scrollHeight="217" style="width: 100%;">  
          <f:facet name="header">  
            <p:outputPanel>  
                <h:outputText value="Search all fields: "/>  
                <p:inputText id="globalFilter" onkeyup="dataTable.filter()"/>  
            </p:outputPanel>  
          </f:facet> 
          <p:column selectionMode="multiple"/>  
          <p:column id="time" headerText="Time" sortBy="#{scrshot.time}" filterBy="#{scrshot.time}" filterMatchMode="startsWith">  
            <h:outputText value="#{scrshot.time}"/>  
          </p:column>   
          <p:column id="id" headerText="ID" sortBy="#{scrshot.id}" filterBy="#{scrshot.id}" filterOptions="#{scrshot.id}" filterMatchMode="exact">  
            <h:outputText value="#{scrshot.id}"/>  
          </p:column>  
    </p:dataTable>

Answer 1

Well in the case of lazy loader you will have to set total count of you records like “this.setRowCount(total_records_that_are_there);” in your “load” method. It is necessary for the lazy loader to determine how much pages there will be so that the next and previous buttons on data table can be determined i.e (Enable/disable). Like [0 is start] and [total/rowsize] is the total number of pages however you fetch using the load method with (first and pagezie => skip and limit);