Unfortunately, there is no way to use our indexed crawler to search by attribute value. You will have to search by ElementTemplate and then process the returned collection on the client side in order to select the element whose attribute value is equal to what you want.
Thanks for the response. This is what I figured I would have to do to get my answer. Do you know if this maybe a feature in a future release?
I have talked to the developers and currently it is not on the list of enhancement for future releases. But I will send another e-mail to them with your request.
There is an AFSDK method, AFElement.FindElementsByAttribute(), that can perform the search that you described, though it might not be exposed via the PI Web API. Make sure to set the IsIndexed property on the AttributeTemplate and search performance will be improved.