h:selectOneMenu in p:dataTable doesn't submit its value - jsf

Question

I have a question about selectOneMenu and settting the values. I have an Object SampleDesc that has and ID, Text, and a List<SampleDescValues>. For each datatable row the Text is the output label and the select one menu values are the List<SampleDescValues>.
XHTML:
<h:panelGroup id="tables">
<p:dataTable resizableColumns="true"
var="sampleDesc" id="SampleDescTable" rowIndexVar="rowIndex"
value="#{sampleBean.sampleDescList.list}"
rendered="#{sampleBean.sampleDescList.list.size() gt 0}">
<p:column>
<h:outputLabel value="#{sampleDesc.sampleDescText}"/>
</p:column>
<p:column>
<h:selectOneMenu required="#{sampleBean.sampleDescList.list.size() gt 0}" converter="#{sampleDescValueConverter}"
id="SampleDescValue" value="#{sampleBean.selectedSampleDescList.get(rowIndex)}">
<f:selectItem itemLabel="Select One" itemValue="#{null}"/>
<f:selectItems value="#{sampleDesc.sampleDescValues}" var="sdv"
itemLabel="#{sdv.sampleDescValuesText}" itemValue="#{sdv}" />
</h:selectOneMenu>
</p:column>
</p:dataTable>
</h:panelGroup>
I have the converter setup and it works because ive set it to a single SampleDescValue and it set the value.
The problem is when i try and populate the form with a Sample from the database it can only set one of the dropdowns when there could be an infinite number of selectonemenu's
I set the value selected to private List<SampleDescValue> selectedSampleDescList;
When i try and submit it does nothing, it works when the datatable is not rendered.

Answer 1

Your menu value is wrong:
<h:selectOneMenu value="#{sampleBean.selectedSampleDescList.get(rowIndex)}">
It's not possible to perform a set operation on this EL expression.
Use the brace notation instead:
<h:selectOneMenu value="#{sampleBean.selectedSampleDescList[rowIndex]}">
Note that this expects a non-null selectedSampleDescList. So make sure that you've already properly initialized it with a new ArrayList<>() beforehand. EL won't do that for you. It will only set the list items using List#add(index, object) method.
See also:
Our EL wiki page
Unrelated to the concrete problem, this expression
#{sampleBean.sampleDescList.list.size() gt 0}
can be simplified as follows
#{not empty sampleBean.sampleDescList.list}
And this is unnecessary in the required attribute of the <h:selectOneMenu> as it would always evaluate true at that point. Just use required="true" directly instead.