如何将当前正在编辑的p:dataTable的一行更改通知给相应的后台bean

Question

如何知道在<p:dataTable>中编辑的行的任何列/s的内容是否发生了变化?给出如下简单的例子。

数据表:

<p:dataTable var="brand" value="#{testManagedBean}"
             lazy="true" editable="true" rows="10">
    <p:column headerText="Id">
        <h:outputText value="#{brand.brandId}"/>
    </p:column>
    <p:column headerText="Brand">
        <p:cellEditor>
            <f:facet name="output">
                <h:outputText value="#{brand.brandName}"/>
            </f:facet>
            <f:facet name="input">
                <p:inputText value="#{brand.brandName}"/>
            </f:facet>
        </p:cellEditor>
    </p:column>
    <p:column headerText="Edit" width="50">
        <p:rowEditor/>
    </p:column>
    <p:ajax event="rowEdit" listener="#{testManagedBean.onRowEdit}"/>
</p:dataTable>

被管理bean:

@ManagedBean
@ViewScoped
public final class TestManagedBean extends LazyDataModel<Brand> implements Serializable
{
    @EJB
    private final TestBeanLocal service=null;
    private static final long serialVersionUID = 1L;
    @Override
    public List<Brand> load(int first, int pageSize, String sortField, SortOrder sortOrder, Map<String, Object> filters) {
        setRowCount(3);  //Just an example. Actually fetched from the database.
        return service.getList(first, pageSize, sortField, sortOrder, filters);
    }
    public void onRowEdit(RowEditEvent event) {
        //Do something to check if the row currently being edited has been changed.
        //If something is changed then, invoke an EJB method to propagate changes to the database.
        //If nothing is changed then, get rid of invoking an expensive business service method to unnecessarily execute an update query.
        System.out.println("onRowEdit() called.");
    }
}

是否有一种方法来调用业务服务(更新数据库内容)，当且仅当当前在给定<p:dataTable>中编辑的行实际上被更改?

_{可以在<p:dataTable>中添加更多的列。}

Answer 1

将此属性添加到bean:

private Brand original;

在dataTable中，为rowEditInit事件添加一个监听器:

<p:ajax event="rowEditInit" listener="#{testManagedBean.onRowEditInit()}" />

设置触发rowEditInit事件时的属性值:

public void onRowEditInit(RowEditEvent event) {
    original = (Brand) event.getObject();
}

最后，检查onRowEdit():

public void onRowEdit(RowEditEvent event) {
    Brand modified = (Brand) event.getObject();
    // compare modified against original
}