I'm trying to build a page with a datatable that can display multiple values derived from, but not stored in an SObject. All the examples show the controller extension method returning SObject lists (e.g. Account[], which works just fine), but I want to display some computed values that are not stored in the SObject (e.g. the number of Contacts in the Account).

Normally, I would just declare a bean with the SObject fields plus the computed fields and have the controller return that, but I do not see a way to do this in force.com. All SObjects are persistent and I do not wish to create table fields to store these computed values.

The only way I can think of to proceed is by having the controller extension method return a List<Map<String, String>> instead of SObject[]. I have coded the controller method and it is happy, but when I try to invoke the get() method on the map my page will no longer compile (save error: unknown function obj.get. Check spelling). Here's a fragment...

    public List<Map<String, String>> getSummary(){...}

             <apex:datatable value="{!summary}" var="obj" styleClass="list">
                <apex:column>
                    <apex:facet name="header">Account Name</apex:facet>
                    <apex:outputText>
                        <a href="Detail?id={!obj.get('id')}">{!obj.get('name')}</a>
                    </apex:outputText>
                </apex:column>
                <apex:column>
                    <apex:facet name="header">#Contacts</apex:facet>
                    <apex:outputText>{!obj.get('contacts')}</apex:outputText>
                </apex:column>

Can someone give me a hint about how to proceed?