Order Processing Module Architecture Review

Problem/Feature Description

An e-commerce startup is scaling up its engineering team and wants to establish code quality standards before onboarding three new backend engineers. The tech lead has noticed that the order processing module has grown organically and suspects it has accumulated some structural problems that will slow the new hires down. She wants a written architecture review that can be shared with the team to inform a future refactoring sprint and establish what "healthy Rails code" looks like in this codebase.

The review should focus on the kinds of structural problems that cause bugs as the system grows — misplaced responsibilities, tight coupling, and logic that ends up in the wrong layer — rather than surface-level style preferences. The team wants concrete, ranked findings they can use to plan work, not a catalogue of every possible improvement.

Produce an architecture review of the code below. Save the review as architecture-review.md.

Input Files

The following files are provided as inputs. Extract them before beginning.

=============== FILE: app/controllers/orders_controller.rb =============== class OrdersController < ApplicationController def create @order = Order.new(order_params) @order.user = current_user

ActiveRecord::Base.transaction do
  @order.save!
  @order.line_items.each do |item|
    item.product.decrement!(:stock_quantity, item.quantity)
  end
  payment = PaymentGateway.charge(
    amount: @order.total_cents,
    token: params[:payment_token],
    description: "Order ##{@order.id}"
  )
  @order.update!(payment_reference: payment.id, status: :paid)
  OrderMailer.confirmation(@order).deliver_now
  Segment.track(user_id: current_user.id, event: "order_placed", properties: { order_id: @order.id })
end

redirect_to @order

rescue PaymentGateway::ChargeError => e @order.update(status: :payment_failed) flash[:error] = e.message render :new end

private

def order_params params.require(:order).permit(:shipping_address, :billing_address, line_items_attributes: [:product_id, :quantity]) end end

=============== FILE: app/models/order.rb =============== class Order < ApplicationRecord belongs_to :user has_many :line_items, dependent: :destroy has_many :products, through: :line_items

accepts_nested_attributes_for :line_items

before_save :calculate_total after_create :reserve_inventory after_commit :sync_to_warehouse, on: [:create, :update]

scope :recent, -> { where("created_at > ?", 30.days.ago) } scope :for_reporting, -> { joins(:line_items, :products) .select("orders.*, SUM(line_items.quantity * products.unit_price) as computed_total, COUNT(line_items.id) as item_count") .group("orders.id") .having("SUM(line_items.quantity * products.unit_price) > 0") }

def calculate_total self.total_cents = line_items.sum { |i| i.quantity * i.product.unit_price_cents } end

def reserve_inventory line_items.each { |i| i.product.decrement!(:reserved_quantity, i.quantity) } end

def sync_to_warehouse WarehouseApi.push_order(self.as_json(include: :line_items)) end end

=============== FILE: app/models/concerns/auditable.rb =============== module Auditable extend ActiveSupport::Concern

included do after_create :log_creation after_update :log_changes after_destroy :log_deletion end

def log_creation AuditLog.create!(event: "created", record_type: self.class.name, record_id: id, payload: self.as_json) Slack.notify("#audit", "#{self.class.name} #{id} created") UserMailer.admin_alert("Record created: #{self.class.name} #{id}").deliver_later end

def log_changes AuditLog.create!(event: "updated", record_type: self.class.name, record_id: id, payload: self.previous_changes) Slack.notify("#audit", "#{self.class.name} #{id} updated") end

def log_deletion AuditLog.create!(event: "deleted", record_type: self.class.name, record_id: id, payload: {}) Slack.notify("#audit", "#{self.class.name} #{id} deleted") end end