PrimeFaces editable cell doesn't update the value - jsf

Question

So I am trying to use a PrimeFaces data table to set data to a list as follows;
<h:form id="frmSalarySupplement">
<p:panel>
<p:dataTable id="tblSalarySupplement"
value="#{salSupplementMB.dataListFromDB}"
var="salSupp"
rowIndexVar="rowSn"
scrollable="true"
rows="10"
paginator="true"
editable="true"
editMode="cell"
rowsPerPageTemplate="10,20,50,100">
<p:ajax event="cellEdit"
listener="#{salSupplementMB.onCellEdit}"
update="#this" />
<p:column headerText="#" escape="false"
style="white-space:pre-line;
word-break:break-all;
width:20px;
text-align:center;">
<h:outputText value="#{rowSn+1}" />
</p:column>
<p:column headerText="Name"
style="white-space:pre-line;
word-break:break-all;
width:250px;">
<h:outputText value="#{salSupp.empId.name}" />
</p:column>
<p:column headerText="Designation"
style="white-space:pre-line;
word-break:break-all;
width:150px;">
<h:outputText value="#{salSupp.empId.designation.designationName}" />
</p:column>
<p:column headerText="Allowance"
style="white-space:pre-line;
word-break:break-all;
width:100px;">
<p:cellEditor>
<f:facet name="input">
<h:inputText value="#{salSupp.allowance}"
style="width:100%" />
</f:facet>
<f:facet name="output">
<h:outputText value="#{salSupp.allowance}" />
</f:facet>
</p:cellEditor>
</p:column>
<p:column headerText="Special
Allowance"
style="white-space:pre-line;
word-break:break-all;
width:100px;">
<p:cellEditor>
<f:facet name="input">
<h:inputText value="#{salSupp.specialAllowance}"
style="width:100%" />
</f:facet>
<f:facet name="output">
<h:outputText value="#{salSupp.specialAllowance}" />
</f:facet>
</p:cellEditor>
</p:column>
<p:column headerText="Transport
Allowance"
style="white-space:pre-line;
word-break:break-all;
width:100px;">
<p:cellEditor>
<f:facet name="input">
<h:inputText value="#{salSupp.transportAllowance}"
style="width:100%" />
</f:facet>
<f:facet name="output">
<h:outputText value="#{salSupp.transportAllowance}" />
</f:facet>
</p:cellEditor>
</p:column>
</p:dataTable>
</p:panel>
</h:form>
So I want to be able to save the data I have edited on the cell to set it on the list. When I do the following, I don't get an updated value.
public void onCellEdit(CellEditEvent event) {
Object oldValue = event.getOldValue();
Object newValue = event.getNewValue();
}
Can someone suggest what shall I do with it?
Update
Also, can anyone tell me why my table loads multiple times when I edit the value? Maybe that's what's giving me the problem.