code: private File fileExists(final String path, final long checksum) throws FrameworkException {
  
  		final PropertyKey<Long> checksumKey = StructrApp.key(File.class, "checksum");
  		final PropertyKey<String> pathKey   = StructrApp.key(File.class, "path");
  
  		return app.nodeQuery(File.class).and(pathKey, path).and(checksumKey, checksum).getFirst();
  	}
docs: Check whether a file with given path and checksum already exists