Selected row is null using different forms - primefaces

Question

I am getting a null selected row when I press the showDialog command button
I can't see what is my problem
This is my first form:
<h:form id="firstForm">
<p:commandButton action="#{testBB.showDialog}" id="showDialog"
update=":secondForm" value="#{msg['show.dialog']}" />
</h:form>
This is my second form:
<h:form id="secondForm">
<p:dataTable id="testDatatable"
rendered="#{not empty testBB.list}"
rowKey="#{order.orderNumber}"
selection="#{testBB.selectedRow}"
selectionMode="single"
sortBy="customerName" value="#{testBB.list}" var="order">
<p:column headerText="#{msg['order.number']}">
<h:outputText value="#{order.orderNumber}" />
</p:column>
<p:column headerText="#{msg['total.value']}">
<h:outputText value="#{order.totalValue}" />
</p:column>
</p:dataTable>
</h:form>
My backing bean:
#ManagedBean
#ViewScoped
public class TestBB implements Serializable {
private List<Order> list;
private Order selectedRow;
public void showOrder() {
try {
System.out.println(selectedRow);
} catch (Exception exception) {
}
}
}
And my DTO:
public class Order implements Serializable {
private int orderNumber;
private double totalValue;
public void showOrder() {
try {
System.out.println(selectedRow);
} catch (Exception exception) {
}
}
/** Getters and setters */
}
What is wrong in my code?

Answer 1

Put
<p:ajax event="rowSelect" />
<p:ajax event="rowUnselect" />
inside your datatable for selection/unselection to happen as soon as click happens.
If you need selection only on button click use 'process' like this
<p:commandButton process=":secondForm:testDatatable" update=":secondForm"/>

Answer 2

You need to update the model on rowSelection. This can be done using a <p:ajax event="rowSelect" />. Here is how I think your Datatable should look like:
<p:dataTable id="testDatatable"
rendered="#{not empty testBB.list}"
rowKey="#{order.orderNumber}"
selection="#{testBB.selectedRow}"
selectionMode="single"
sortBy="customerName" value="#{testBB.list}" var="order">
<p:ajax event="rowSelect" />
<p:column headerText="#{msg['order.number']}">
<h:outputText value="#{order.orderNumber}" />
</p:column>
<p:column headerText="#{msg['total.value']}">
<h:outputText value="#{order.totalValue}" />
</p:column>
</p:dataTable>
A good example can be found here (Primefaces Demo).

Answer 3

As Kerem Baydogan suggested you have to include process attribute with your data table id in your command button.
If you are not including process attribute then no components will be processed in the component tree and no modal values will be updated hence you are getting selection as null.
I feel there is no need of updating data table if you are not changing its state.