Feeds: use custom field as unique field for mapping I am using D7, Feeds, XPath Parser.
For mapping, I need to use a custom field as the unique field. I am retreiving data from booking.com and the unique value their is the hotel id, so i need to save this hotel id from the user as well as retrieve data from booking.com bsed on this unique field and map to my contents based on this unique field.

In the documentation of feeds i found this - 
Use field other than nid as unique node field in feeds for 7.x-2.x

It says you need to apply a patch from this comment - http://drupal.org/node/661606#comment-5921904

This patch applies to a file called field.inc in the mappers folder of feeds. However this file is not even present there.
The patch also applies to another file, however running the patch gives errors.


Is field.inc actually present in feeds/mappers? 
Am I making some mistake in applying the patch?
Is there any other way of achieving  - custom field as unique field for mapping?


Any help on this would be greatly appreciated. Thank you.
This tutorial works for me:

How to configure unique fields in Drupal feeds importer ?

See also the official documentation, which states that you can either use the Field Validation module, or write a custom solution implementing hook_feeds_processor_targets_alter().