Maybe/app/controllers/transfers_controller.rb

class TransfersController < ApplicationController
  layout "with_sidebar"

  before_action :set_transfer, only: :destroy

  def new
    @transfer = Transfer.new
  end

  def create
    from_account = Current.family.accounts.find(transfer_params[:from_account_id])
    to_account = Current.family.accounts.find(transfer_params[:to_account_id])

    @transfer = Transfer.build_from_accounts from_account, to_account, \
                                             date: transfer_params[:date],
                                             amount: transfer_params[:amount].to_d,
                                             currency: transfer_params[:currency],
                                             name: transfer_params[:name]

    if @transfer.save
      redirect_to transactions_path, notice: t(".success")
    else
      render :new, status: :unprocessable_entity
    end
  end

  def destroy
    @transfer.destroy_and_remove_marks!
    redirect_back_or_to transactions_url, notice: t(".success")
  end

  private

    def set_transfer
      @transfer = Transfer.find(params[:id])
    end

    def transfer_params
      params.require(:transfer).permit(:from_account_id, :to_account_id, :amount, :currency, :date, :name)
    end
end