class CustomersController < ApplicationController
    # …
    def create
        @customer = Customer.new(customer_params)

        respond_to do |format|
            if @customer.save
                format.html { redirect_to @customer,
                                            notice: 'Customer was successfully created.' }
                format.json { render :show, status: :created,
                                            location: @customer }
            else
                format.html { render :new }
                format.json { render json: @customer.errors,
                                                         status: :unprocessable_entity }
            end
        end
    end
    # …
end