How to get attachment file name of a work item in a customized attribute

 How to run a query in calculated value or value set?

the only approach that might work is described here: http://jorgediazblog.wordpress.com/2012/06/27/work-item-customization-httpconector-and-oauth-in-rtc-4-0-for-oslc/
You would have to use REST/OSLC to access the query.

 2. Create an attribute ’TestField1’

Also it works by following:

        var params= new com.ibm.team.workitem.api.common.connectors.HttpConnectorParameters();
        params.url="https://vappwin2k8r2ja:9443/ccm/oslc/workitems/15/rtc_cm:com.ibm.team.workitem.linktype.attachment.attachment";
        params.xpath= "//Collection/Attachment";
        params.columnXpaths= ["./title"];
        params.columnIds= ["title"];
        params.ignoreInvalidCertificates=true;
        params.useOAuth=true;

        var connector= context.getDataConnector("HttpConnector");
        var values= connector.get(params);
        var result= [];

         while(values.hasNext()){ 
            var entry= values.next(); 
            var wiIDs= entry.getById("title"); 
            result.push(wiIDs); 
        } 

        return result; 
    } 
   }); 
})();