Eager load line item details on the admin order page to avoid N+1s

admin/app/controllers/solidus_admin/orders_controller.rb

@@ -36,7 +36,7 @@ def new
     end
 
     def show
-      load_order
+      load_order(Spree::Order.includes(line_items: {variant: [:images, {product: :variant_images, option_values: :option_type}]}))
 
       respond_to do |format|
         format.html { render component("orders/show").new(order: @order) }
@@ -111,8 +111,8 @@ def customers_for
 
     private
 
-    def load_order
-      @order = Spree::Order.find_by!(number: params[:id])
+    def load_order(scope = Spree::Order)
+      @order = scope.find_by!(number: params[:id])
       authorize! action_name, @order
     end
 

admin/spec/requests/solidus_admin/orders_spec.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+RSpec.describe "SolidusAdmin::OrdersController", type: :request do
+  let(:admin_user) { create(:admin_user) }
+
+  before do
+    allow(SolidusAdmin::Config).to receive(:enable_alpha_features?).and_return(true)
+    allow_any_instance_of(SolidusAdmin::BaseController).to receive(:spree_current_user).and_return(admin_user)
+  end
+
+  describe "GET #show" do
+    let(:order) { create(:completed_order_with_totals, line_items_count: 3) }
+
+    it "renders successfully" do
+      get solidus_admin.order_path(order)
+      expect(response).to have_http_status(:ok)
+    end
+
+    it "loads line item variants in a single query" do
+      expect { get solidus_admin.order_path(order) }
+        .to make_database_queries(matching: /from .spree_variants..*\bid. IN \(/im, count: 1)
+    end
+  end
+end