PostValidate datatable list values - jsf

Question

I have a list of items that are being displayed using a h:datatable like so:
<p:dataTable value="#{myBean.instructorsList}" var="ins">
<p:column headerText="Name">
<h:inputText value="#{ins.name}"/>
</p:column>
</p:dataTable>
My spec is that I cannot allow a instructor to have the same name as another insturctor. So I need to have access to all the entire instructorList when it is submitted. I have attempted to validate using a postValidate f:event however due to the JSF lifecycle it does not update the model values till after the postValidation phase.
My attempt
<f:event listener="#{myBean.myMethod}" type="postValidate" />
Backing code
private List<instructors> instructorsList;
public void myMethod(ComponentSystemEvent event) {
// Attempting to use the instructorsList with new values. However, this
// is at the wrong stage
}
How would I write a validator to accomplish checking for duplicate instructor names?

Answer 1

Within a listener, use the getSubmittedValue method on HtmlInputText to pull the value straight off the component. Also, postValidate is semantically late to call problems on the validation process. Use the preValidate method instead. Altogether, you should have
public void myMethod(ComponentSystemEvent event) {
HtmlInputText txtBox = (HtmlInputText)event.getComponent();
String theValue = txtBox.getSubmittedValue().toString(); //the value in the textbox
//based on the outcome of your validation, you also want to do the following
FacesContext.getCurrentInstance().setValidationFailed(); //flag the entire request as failing validation
txtBox.setValid(false); //mark the component as failing validation
}
EDIT: This approach is heavily hinged on the premise that your users will be submitting only one row at a time. In the case where the entire table/column is being submitted in one request, you'll find that evaluating each input field on by one doesn't do much to prevent race conditions; you should be looking toward cross-field validation instead.
EDIT 2: I was mistaken, you cannot have race conditions when the event listener is being called. The listener is executed for each row, sequentially. This allows you to safely check each row (perhaps against a Map, for duplicates), without worrying about race conditions.