DataSink Multiple Nodes from property transfer

Hi All,

Using pro trail version to test features. How can extract 'buildingRef key' all nodes and print them to a flat file. i.e.

CSV file - 20001,20002,20003

I can only manage to extract 1 node link this: -
//place[1]/buildingRef[1]/@key

Below is the reposne: -

<place placeCode="LON" channel="SON">
<buildingRef key="20001"/>
<buildingRef key="20002"/>
<buildingRef key="20003"/>
</place>

Your expertise is most appreciated

Thanks