Where does a data-import map go?

Hello,
I'm writing an application that will need to import a complex dataset in JSON format (via file upload) to a database. A human will have to perform a step of mapping JSON keys to DB fields because the data structure is variable. 
What is the best approach for organizing the code for these operations? I have already a controller that manages the upload; where should it go from there? Before being passed to a model for db saving, where should the pre and post human processing take place? A library? A service? Private methods of the upload controller?
Thanks,
Evan