How to always pre-fill nested form attributes with Reform stone?

Question

How to always pre-fill nested form attributes with Reform stone?

I have a model Financingwith has_many: :professional_investments.

To edit Financing, the main form has a nested form for professional_investments.

I decided to display a fixed list of 8 professional_investments, since the gem Cocoondoes not work very well with Trailblazer Reform.

I use two form objects Reform: a FinancingFormand nested ProfessionalInvestmentForm:

class FinancingForm < Reform::Form
  collection :professional_investments,
    form: ProfessionalInvestmentForm,
    prepopulator: :prepopulate_professional_investments,
    populate_if_empty: :populate_professional_investments!,
    skip_if: :professional_investment_blank?

  def prepopulate_professional_investments(options)
    [8 - professional_investments.size, 0].max.times do
      professional_investments << ProfessionalInvestment.new
    end
  end

  def populate_professional_investments!(fragment:, **)
    ProfessionalInvestment.new unless professional_investment_blank?(fragment: fragment)
  end

  def professional_investment_blank?(fragment:, **)
    fragment['professional_investor_id'].blank? && fragment['amount'].to_d.zero?
  end
end

In the controller, I create a form object and pre-populate it:

class FinancingsController < ApplicationController
  def edit
    @financing_form = FinancingForm.new(@financing)
    @financing_form.prepopulate!
  end

  def update
    @financing_form = FinancingForm.new(@financing)
    @financing_form.prepopulate!
    if @financing_form.validate(financing_params)
      @financing_form.save
    end
  end
end