SharePoint 2013 REST API: how to get or set document fields

I want to get and also set document properties defined in a content type via a Rest call in either and app or a workflow Activity.

If you fire up Google Postman or Advanced REST Api client you can get a desired json response for the query below

   http://mydev/sites/test/_api/web/getFileByServerRelativeUrl('/sites/test/Shared Documents/Integration.pdf')/Name

.... now I want the more useful fields such as lookups or Managed Metadata values that are also held against my file via a content type.

         /CustomerRef

seems I need another approach as the the field exists in the view but I am not able to get it in my response . Any ideas how I do this please. I have tried ?expand=ContentType