<c:when> not working in PrimeFaces datatable? - jsf

Question

What I'm trying to do is do something to the first row, second row, etc. of the table.
<p:panel header="#{mat.description}">
<p:dataTable var="datarow" value="#{myBean.getDatarows(mat.itemId)}" emptyMessage="No materials" rowIndexVar="row">
<c:choose>
<c:when test="${row eq 0}">
<p:column headerText=""><h:outputText value="#{datarow.get(1)}" /></p:column>
</c:when>
<c:when test="${row eq 1}">
<p:column headerText=""><h:outputText value="#{datarow.get(1)}" /></p:column>
</c:when>
</c:choose>
<p:column headerText=""><h:outputText value="#{datarow.get(6)}" /></p:column>
<p:column headerText="Month 1"><h:outputText value="#{datarow.get(1)}" /></p:column>
<p:column headerText="Month 3"><h:outputText value="#{datarow.get(2)}" /></p:column>
<p:column headerText="Month4"><h:outputText value="#{datarow.get(3)}" /></p:column>
<p:column headerText="Month 5"><h:outputText value="#{datarow.get(4)}" /></p:column>
<p:column headerText="Month6"><h:outputText value="#{datarow.get(5)}" /></p:column>
</p:dataTable>
</p:panel>
But the c:choose and c:when is not displaying anything. Am I doing the test for row number wrongly?

Answer 1

This is bad design and will not work that way. You are mixing up JSTL and JSF tags in a wrong way.
The JSTL tags c:choose and c:when are evaluated during tree built, but the p:dataTable tag when the UI tree is rendered.
Just use the rendered-attribute on p:column instead, if you want to include/exclude complete columns of your datatable. If you want to achieve different behavior of what is beeing displayed inside the columns, you could for example use the ?-operator to decide what is beeing rendered:
<p:dataTable var="datarow" ... rowIndexVar="row">
<p:column>
<h:outputText value="#{row eq 0 ? datarow.get(1) : 'some other stuff'}"/>
</p:column>
</p:dataTable>
To render different kind of elements inside your column, just put both of them inside the column, but with different rendered-attribute:
<p:column>
<h:outputText rendered="#{row != 4}"/>
<p:inputText rendered="#{row eq 4}"/>
</p:column>
This will render an input-element in the 5th row (rowIndexVar is 0-based), and an output-element in all other rows.

Answer 2

I believe you always need the same number of columns.
Change your code to:
<c:when test="${row eq 0}">
<p:column headerText=""><h:outputText value="#{datarow.get(1)}" /></p:column>
</c:when>
<c:when test="${row ne 0}">
<p:column headerText=""><h:outputText value="#{datarow.get(1)}" /></p:column>
</c:when>
This way you still have the column when not in the first or second row.