Improve product drive index page performance

app/controllers/product_drives_controller.rb

@@ -7,7 +7,7 @@ def index
     setup_date_range_picker
     @product_drives = current_organization
                      .product_drives
-                     .includes(:tags, donations: {line_items: :item})
+                     .includes(:tags)
                      .class_filter(filter_params)
                      .within_date_range(@selected_date_range)
                      .order(start_date: :desc)
@@ -17,12 +17,17 @@ def index
     @selected_name_filter = filter_params[:by_name]
     @selected_item_category = filter_params[:by_item_category_id]
     @selected_tags = filter_params[:by_tags]
+    @summary = ProductDriveSummaryService.call(
+      product_drives: @product_drives,
+      within_date_range: helpers.selected_interval,
+      item_category_id: @selected_item_category
+    )
 
     respond_to do |format|
       format.html
       format.csv do
         send_data Exports::ExportProductDrivesCSVService.new(
-          @product_drives,
+          @product_drives.unscope(:includes).includes(donations: {line_items: :item}),
           current_organization,
           helpers.selected_range
         ).generate_csv, filename: "Product-Drives-#{Time.zone.today}.csv"

app/models/product_drive.rb

@@ -20,7 +20,7 @@ class ProductDrive < ApplicationRecord
 
   scope :by_name, ->(name_filter) { where(name: name_filter) }
   scope :by_item_category_id, ->(item_category_id) {
-    joins(donations: {line_items: :item})
+    includes(donations: {line_items: :item})
       .where(item: { item_category_id: item_category_id })
   }
 

app/services/product_drive_summary_service.rb

@@ -0,0 +1,40 @@
+# Calculates the quantity, unique item count, and value for product
+# drives from donations (filtered by items donated in a given date range
+# and within a given item category if provided).
+class ProductDriveSummaryService
+  class << self
+    ProductDriveSummary = Data.define(:quantity, :unique_item_count, :value)
+    NULL_PRODUCT_DRIVE_TOTALS = ProductDriveSummary.new(quantity: 0, unique_item_count: 0, value: 0)
+
+    def call(product_drives:, within_date_range:, item_category_id: nil)
+      calculate_totals(product_drives, within_date_range, item_category_id)
+    end
+
+    private
+
+    # @return [Hash<Integer, ProductDriveSummary>]
+    def calculate_totals(product_drives, within_date_range, item_category_id)
+      query = ProductDrive
+        .left_joins(donations: {line_items: [:item]})
+        .where(id: product_drives.ids)
+        .where(donations: {issued_at: within_date_range[0]..within_date_range[1]})
+        .group("product_drives.id")
+        .distinct
+
+      query = query.where(items: {item_category_id: item_category_id}) if item_category_id.present?
+
+      totals = query.pluck(Arel.sql(
+        "product_drives.id AS id,
+        COALESCE(SUM(line_items.quantity), 0) AS quantity,
+        COUNT(DISTINCT line_items.item_id) AS unique_item_count,
+        COALESCE(SUM(COALESCE(items.value_in_cents, 0) * line_items.quantity), 0) AS value"
+      )).to_h do |(id, quantity, unique_item_count, value)|
+        [id, ProductDriveSummary.new(quantity:, unique_item_count:, value:)]
+      end
+
+      # If a product drive has no matching donations/items, set totals to
+      # default values (zeroes).
+      product_drives.ids.to_h { |id| [id, NULL_PRODUCT_DRIVE_TOTALS] }.merge(totals)
+    end
+  end
+end

app/views/product_drives/index.html.erb

@@ -109,9 +109,9 @@
                   <td><%= product_drive.end_date&.strftime("%m-%d-%Y") %></td>
                   <td><%= product_drive.tags_for_display %></td>
                   <td><%= is_virtual(product_drive: product_drive) %></td>
-                  <td class="text-right"><%= product_drive.donation_quantity_by_date(selected_range, @selected_item_category) %></td>
-                  <td class="text-right"><%= product_drive.distinct_items_count_by_date(selected_range, @selected_item_category) %></td>
-                  <td class="text-right"><strong><%= dollar_value(product_drive.in_kind_value) %></strong></td>
+                  <td class="text-right"><%= @summary[product_drive.id].quantity %></td>
+                  <td class="text-right"><%= @summary[product_drive.id].unique_item_count %></td>
+                  <td class="text-right"><strong><%= dollar_value(@summary[product_drive.id].value) %></strong></td>
                   <td class="text-right"><%= view_button_to product_drive_path(product_drive.id) %></td>
                 </tr>
               <% end %>