Don't persist line item actions in compute_amount

This method will be used in the in memory order updater. We only want to
persist to the database once we perform the action, not when we are
computing the amount.

Author: AlistairNorman

legacy_promotions/app/models/spree/promotion/actions/create_quantity_adjustments.rb

@@ -75,14 +75,19 @@ def compute_amount(line_item)
             line_item.quantity
           ].min
 
-          persist_quantity(usable_quantity, line_item)
+          set_line_item_action_quantity(usable_quantity, line_item)
 
           amount = adjustment_amount * usable_quantity
           [line_item.amount, amount].min * -1
         end
 
         private
 
+        def create_adjustment(adjustable, order, promotion_code)
+          return unless super
+          save!
+        end
+
         def actionable_line_items(order)
           order.line_items.select do |item|
             promotion.line_item_actionable? order, item
@@ -97,17 +102,16 @@ def total_applicable_quantity(line_items)
         end
 
         def total_used_quantity(line_items)
-          line_item_actions.where(
-            line_item_id: line_items.map(&:id)
-          ).sum(:quantity)
+          line_item_actions.select { |line_item_action|
+            line_items.map(&:id).include? line_item_action.line_item_id
+          }.sum(&:quantity)
         end
 
-        def persist_quantity(quantity, line_item)
+        def set_line_item_action_quantity(quantity, line_item)
           line_item_action = line_item_actions.where(
             line_item_id: line_item.id
           ).first_or_initialize
           line_item_action.quantity = quantity
-          line_item_action.save!
         end
 
         ##

legacy_promotions/spec/models/spree/promotion/actions/create_quantity_adjustments_spec.rb

@@ -22,6 +22,48 @@ module Spree::Promotion::Actions
     let(:quantity) { 1 }
     let(:promotion) { FactoryBot.create :promotion }
 
+    describe "#perform" do
+      subject { action.perform({ order:, promotion: }) }
+
+      let(:calculator) { FactoryBot.create :flat_rate_calculator, preferred_amount: }
+
+      context "when calculator computes 0" do
+        let(:preferred_amount) { 0 }
+
+        it "does not create an adjustment" do
+          expect { subject }
+            .not_to change { action.adjustments.count }
+        end
+      end
+
+      context "when calculator returns a non-zero value" do
+        let(:preferred_amount) { 10 }
+        let(:line_item) { order.line_items.first }
+
+        it "creates an adjustment" do
+          expect { subject }
+            .to change { action.adjustments.count }
+            .from(0).to(1)
+            .and change { line_item.adjustments.count }
+            .from(0).to(1)
+
+          expect(line_item.adjustments).to eq(action.adjustments)
+        end
+
+        it "associates the line item with the action", :aggregate_failures do
+          expect { subject }
+            .to change { line_item.line_item_actions.count }
+            .from(0).to(1)
+
+          expect(action.line_item_actions.first).to have_attributes(
+            line_item_id: line_item.id,
+            action_id: action.id,
+            quantity: 1
+          )
+        end
+      end
+    end
+
     describe "#compute_amount" do
       subject { action.compute_amount(line_item) }
 
@@ -46,6 +88,15 @@ module Spree::Promotion::Actions
           context "and an item with a quantity of 2" do
             let(:quantity) { 2 }
             it { is_expected.to eq(-10) }
+
+            it "doesn't save anything to the database" do
+              action
+              line_item
+
+              expect {
+                subject
+              }.not_to make_database_queries(manipulative: true)
+            end
           end
 
           context "and an item with a quantity of 3" do
@@ -94,7 +145,7 @@ module Spree::Promotion::Actions
               :order_with_line_items,
               line_items_attributes: [
                 { quantity: 3 }
-            ]
+              ]
             )
           end