Upgraded from Drupal 6 to 7 or have a early Drupal 7 installation and there are a high change that you might still use the legacy Media field. This field used to be the only field that allowed us to use the media widget. It have since been replaced by a standard file/image field, provided by Drupal 7 core. Media also need the third part module, File entity (file_entity - https://www.drupal.org/project/file_entity). This module extends core file entity functionality.
This is probably the last post in this series. I will try in this article to bring it all together. This will also be the most code heavy article. If you are new to migrate and Drupal-to-Drupal data migration, make sure you read and understand the first articles before preceding.
Mapping fields (field mappings)
Migrate have no way of knowing your plans for your Drupal 6 CCK fields or to what fields you are planning to store the data in Drupal 7. Perhaps you do not want or need to migrate all your old data. Source and target field have the same field name and type, but sometime you might want to fix a bad decisions made in the past and reorganize your architecture. Migrate call this field mappings. What ever reason you might have, you will need to share these ideas with Mirate. The basic format is like this:
This series would be incomplete without also covering node migration. The example code is working code and should import data from drupal 6 to 7 if you have correctly configured your test setup by following the previously articles (part 1-3). Do not be scared by the code. It is more PHP defining stuff then "real" code containing a lot of logic and stuff.