class CheckoutsController < ApplicationController
  ...

  def create
    @checkout = @item.checkouts.build(checkout_params)
    respond_to do |format|
      if @checkout.save
        if @checkout.reservation == true
          @checkout.create_activity :reservation, options = { owner: Person.find(@checkout.checked_out_by), recipient: @item, approved_by_id: @user.id }
        else
          @checkout.create_activity :create, options = { owner: Person.find(@checkout.checked_out_by), recipient: @item, approved_by_id: @user.id }
        end
        format.html { redirect_to checkouts_path, notice: 'Checkout was successfully created.' }
        format.json { render json: @checkout, status: :created, location: @checkout }
      else
        format.html { render :new }
        format.json { render json: @checkout.errors, status: :unprocessable_entity }
      end
    end

    ...
  end