Add option to hash plugin to hash multiple fields.

I realize now that the hash is being created on only one field. I thought the hash was being created on the entire record. It would be great if you could select more than 1 field to create a hash on since it is often the case that more than one field is often required to uniquely identify a record in a database. Working on this...

I tried changing:

function feeds_tamper_hash_callback($result, $item_key, $element_key, &$field, $settings){
if($settings['overwrite'] || !trim($field)){
$field = md5(serialize($result->items[item_key]));
}
}

to

function feeds_tamper_hash_callback($result, $item_key, $element_key, &$field, $settings){
if($settings['overwrite'] || !trim($field)){
$field = md5(serialize($result->items));
}
}

but that didn't seem to have any affect. Is $item_key the field that's being hashed? Is $field the variable that saves the hash in the GUID target field? If anyone can lead me in the right direction, I'd really appreciate it.

I think what might be happening is that the Feeds module is overwriting the hash with the field that maps to the GUID. For example, I have the source field from my upload file: Full Reference Information mapped to GUID. I select this as a unique identifier. Without Feeds Tamper, this field would be my GUID. With Feeds Tamper, I set this field to calculate a hash. But it only treats the record as unique if the the Full Reference Information field is unique, not if the whole record is unique. It doesn't seem to matter if I use $field = md5(serialize($result->items[item_key])); or $field = md5(serialize($result->items));

Here are my settings:

Processor Settings: Do not update existing nodes
Mapping settings: Source: Full Reference Information, Target: GUID, Unique Target selected
Feeds Tamper: Enable hash plugin on Full Reference Information -> Full Reference Information, GUID

Another thought...maybe determining whether or not a field is unique is performed and processed by the Feeds module before Feeds Tamper creates the hash for the node.

If so, I think a patch along the lines of this thread might be needed.
http://drupal.org/node/661606#comment-5648628

I confirmed that a hash of the GUID is NOT being saved in the database table feeds_item. Only the original unhashed single field mapping is being saved.

I now realize that NONE of the Feeds Tamper plugins are working!? In the feeds_tamper.module, line 54: if (isset($item[$element_key])) is always false and none of the plugins ever get called. Any idea why that might happen?