form element names with multiple new rows

I have a report with many rows some of which refer to an existing ActiveRecord model object and some new ones. I'm trying to figure out a naming convention for the form elements so that Rails will properly convert it into a params hash in my controller.

My first idea is to do something like the below but Rails will confuse the data for the two 'new' rows Enter a new invitation <input name=invite[first_name]> <input name=invite[last_name]> <br/> Enter a new invitation <input name=invite[first_name]> <input name=invite[last_name]> <br/> Update an existing invitation <input name=invite[1][first_name]> <input name=invite[1][last_name]> <br/>

My second idea is to do something like the below and parse out the 'new_' params in my controller Enter a new invitation <input name=invite[new_1][first_name]> <input name=invite[last_name]> <br/> Enter a new invitation <input name=invite[new_2][first_name]> <input name=invite[last_name]> <br/> Update an existing invitation <input name=invite[1][first_name]> <input name=invite[1][last_name]> <br/>

Is this a common problem that others have solved in a standard way before? Any pointers to plugins or techniques others have used?

Thanks Alex