I'm trying to build a form that allows users to update some records. They can't update every field, though, so I'm going to do some explicit processing (in the controller for now) to update the model vis-a-vis the form. Here's how I'm trying to do it:

Family model:

class Family < ActiveRecord::Base
  has_many :people, dependent: :destroy
  accepts_nested_attributes_for :people, allow_destroy: true, reject_if: ->(p){p[:name].blank?}
end

In the controller

def check
  edited_family = Family.new(params[:family])
  #compare to the one we have in the db
  #update each person as needed/allowed
  #save it
end

Form:

= form_for current_family, url: check_rsvp_path, method: :post do |f|
  = f.fields_for :people do |person_fields|
    - if person_fields.object.user_editable
      = person_fields.text_field :name, class: "person-label"
    - else
      %p.person-label= person_fields.object.name

The problem is, I guess, that Family.new(params[:family]) tries to pull the people out of the database, and I get this:

ActiveRecord::RecordNotFound in RsvpsController#check

Couldn't find Person with ID=7 for Family with ID=

That's, I guess, because I'm not adding a field for family id to the nested form, which I suppose I could do, but I don't actually need it to load anything from the database for this anyway, so I'd rather not. I could also hack around this by just digging through the params hash myself for the data I need, but that doesn't feel a slick. It seems nicest to just create an object out of the params hash and then work with it.

Is there a better way? How can I just create the nested object?