Adding and removing multiple associated sub-models dynamically on a single form in Rails

The last couple blog posts have been about PeepNote ... its beginning and its ending.  Now I thought I'd share a snippet of code that I developed for it the form of a simple contact manager.

One of the things Brian pointed out in his concluding remarks about PeepNote that I referred to in my last post was,

As I began interacting more with potential customers I realized that my target audience was not what I thought it was. It wasn’t people like me who were heavily using Twitter for career networking and wanted to keep track of how I met people and what I knew about them. Instead, the only people that would pay for the service were companies. Companies that wanted to use it to track potential customers; a CRM.

Part of the CRM functionality that we had incorporated into PeepNote was to add contact information about your peeps.  The idea of a contact manager is well understood by most audiences and are thus commonly used as a demonstration application.  So, what's special about this one and why I'm I writing about it?

This particular contact manager demonstrates (and improves upon) Ryan Bates “Handle Multiple Models in One Form” recipe (#13) from the Advanced Rails Recipes book.  In Ryan’s original recipe, he added discrete field values (individual tasks on a to-do list) to the form. Any tasks that did not have an identifier associated with it was a new task, and any missing task identifiers from those currently in the database were assumed to be deleted.  This is great when you're essentially adding single values to a list, but what about adding multiple pieces of information that need to stay together as a single entity (like the parts of a contact information - street address, city, state, phone, etc)?

The solution is to use a JavaScript variable to assign temporary unique identifiers to newly added nested models (addresses, phone numbers, urls, etc). These newly added models are assigned a negative value in order for the contact controller to distinguish between new and existing records.  So, new records with a negative id are added, existing records are updated as necessary, and any records with ids that are no longer in the submitted list are removed.

This is one of the problems I solved for PeepNote and have extracted into a simple stand-alone Rails application.   Rather than provide a lengthy description here, I placed the source code on GitHub and have a running demo on Heroku.