Datatable does not sort elements in primefaces

问题:

Any idea why the sorting does not work?

<h:form prependId="false">

<p:dataTable value="#{questionBackingBean.questions}"
        var="question" id="questionTable" paginator="true" rows="15"
        paginatorTemplate="{CurrentPageReport}  {FirstPageLink} {PreviousPageLink} {PageLinks} {NextPageLink} {LastPageLink} {RowsPerPageDropdown}"
        rowsPerPageTemplate="15,25,50" paginatorPosition="bottom">


<p:column sortBy="#{question.id}">
    <f:facet name="header">ID</f:facet>
    <h:outputText value="#{question.id}" />
</p:column>
<p:column sortBy="#{question.description}">
    <f:facet name="header">Description</f:facet>
    <h:outputText value="#{question.description}" />
</p:column>
</h:form>

Question entity

@Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + id;
        return result;
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (!(obj instanceof Question)) {
            return false;
        }
        Question other = (Question) obj;
        if (id != other.id) {
            return false;
        }
        return true;
    }

Backing bean

@ManagedBean
@ViewScoped
public class QuestionBackingBean implements Serializable {

    private static final long serialVersionUID = 1L;

    @Inject
    private QuestionLocal questionBean;
    private List<Question> questions;
    @Inject
    private Question question;
    private int questionParamId;

    public List<Question> getQuestions() {
        questions = questionBean.findAllQuestions();

        return questions;
    }

    public void setQuestions(List<Question> questions) {
        this.questions = questions;
    }

    public Question getQuestion() {
        return question;
    }

    public void setQuestion(Question question) {
        this.question = question;
    }

    public int getQuestionParamId() {
        return questionParamId;
    }

    public void setQuestionParamId(int questionParamId) {
        this.questionParamId = questionParamId;
    }

    public void init() {
        question = questionBean.findQuestion(questionParamId);
    }

    public String addQuestion() {
        questionBean.createQuestion(question);
        return "../index.xhtml";
    }
}

回答1:

You are returning a new list everytime getQuestions is called, doing this in JSF is a bad practice and slows down your app as getters are called multiple times in request lifecycle especially in data iteration. Cache your questions list in a property, getter should just return the questions not load them.

Your list is sorted actually in apply request values phase but you return a new instance when a getter is called again in latter phases you the sorted list is gone during processing.

回答2:

You should never put business logic in getter

public List<Question> getQuestions() {
        questions = questionBean.findAllQuestions();

        return questions;
    }

change it to

public List<Question> getQuestions() {
        return questions;
    }

and

public QuestionBackingBean(){
 this.questions = questionBean.findAllQuestions();
};

As you are using @ViewScope the constructor will get called every time you refresh so you have latest data.