Rails 5 Nested Resources for 3 models?

I have 3 models:

Report

has_many :report_items, dependent: :destroy

has_many :items, through: :report_items

Item

has_many :report_items, dependent: :destroy

has_many :reports, through: :report_items

ReportItem

belongs_to :item

belongs_to :report

I scaffolded all 3 models so I now have 3 seperate views for each.

Right now if I wanted to assign an item to a report, I have to:

1. Create new Item record

2. Create new Report record

3. Create new ReportItem record, using the id's of Item and Report to tie them together.

However what I need is for ReportItem to be nested inside Report. The idea is that when I create a new report, I can go to its "show" page and assign items from there.

I've went to http://ift.tt/GVpneB to research on how this would work. However I'm still confused as to how to actually accomplish it.

Any tips on this?