Update cart by applying differences rather than clear-and-readd every time

app/models/spree/order_populator_decorator.rb

@@ -11,13 +11,19 @@ Spree::OrderPopulator.class_eval do
 
     if valid?
       @order.with_lock do
-        @order.empty! if overwrite
-
         variants = read_products_hash(from_hash) +
                    read_variants_hash(from_hash)
 
         variants.each do |v|
-          attempt_cart_add(v[:variant_id], v[:quantity], v[:max_quantity])
+          if varies_from_cart(v)
+            attempt_cart_add(v[:variant_id], v[:quantity], v[:max_quantity])
+          end
+        end
+
+        if overwrite
+          variants_removed(variants).each do |id|
+            cart_remove(id)
+          end
         end
       end
     end
@@ -54,6 +60,11 @@ Spree::OrderPopulator.class_eval do
     end
   end
 
+  def cart_remove(variant_id)
+    variant = Spree::Variant.find(variant_id)
+    @order.remove_variant(variant)
+  end
+
 
   private
 

spec/features/consumer/shopping/shopping_spec.rb

@@ -206,18 +206,29 @@ feature "As a consumer I want to shop with a distributor", js: true do
       end
     end
 
-    describe "adding products to cart" do
+    describe "adding and removing products from cart" do
       let(:exchange) { Exchange.find(oc1.exchanges.to_enterprises(distributor).outgoing.first.id) }
       let(:product) { create(:simple_product) }
       let(:variant) { create(:variant, product: product) }
+
       before do
         add_product_and_variant_to_order_cycle(exchange, product, variant)
         set_order_cycle(order, oc1)
         visit shop_path
       end
-      it "should let us add products to our cart" do
-        fill_in "variants[#{variant.id}]", with: "1"
+
+      it "lets us add and remove products from our cart" do
+        fill_in "variants[#{variant.id}]", with: '1'
         page.should have_in_cart product.name
+        wait_until { !cart_dirty }
+        li = Spree::Order.order(:created_at).last.line_items.order(:created_at).last
+        li.quantity.should == 1
+
+        fill_in "variants[#{variant.id}]", with: '0'
+        within('li.cart') { page.should_not have_content product.name }
+        wait_until { !cart_dirty }
+
+        Spree::LineItem.where(id: li).should be_empty
       end
     end
 

spec/models/spree/order_populator_spec.rb

@@ -9,11 +9,49 @@ module Spree
     let(:order_cycle) { double(:order_cycle) }
     let(:op) { OrderPopulator.new(order, currency) }
 
+    context "end-to-end" do
+      let(:order) { create(:order, distributor: distributor, order_cycle: order_cycle) }
+      let(:distributor) { create(:distributor_enterprise) }
+      let(:order_cycle) { create(:simple_order_cycle, distributors: [distributor], variants: [v]) }
+      let(:op) { OrderPopulator.new(order, nil) }
+      let(:v) { create(:variant) }
+
+      describe "populate" do
+        it "adds a variant" do
+          op.populate({variants: {v.id.to_s => {quantity: '1', max_quantity: '2'}}}, true)
+          li = order.find_line_item_by_variant(v)
+          li.should be
+          li.quantity.should == 1
+          li.max_quantity.should == 2
+        end
+
+        it "updates a variant's quantity and max quantity" do
+          order.add_variant v, 1, 2
+
+          op.populate({variants: {v.id.to_s => {quantity: '2', max_quantity: '3'}}}, true)
+          li = order.find_line_item_by_variant(v)
+          li.should be
+          li.quantity.should == 2
+          li.max_quantity.should == 3
+        end
+
+        it "removes a variant" do
+          order.add_variant v, 1, 2
+
+          op.populate({variants: {}}, true)
+          order.line_items(:reload)
+          li = order.find_line_item_by_variant(v)
+          li.should_not be
+        end
+      end
+    end
+
     describe "populate" do
       before do
         op.should_receive(:distributor_and_order_cycle).
           and_return([distributor, order_cycle])
       end
+
       it "checks that distribution can supply all products in the cart" do
         op.should_receive(:distribution_can_supply_products_in_cart).
           with(distributor, order_cycle).and_return(false)
@@ -22,13 +60,6 @@ module Spree
         op.errors.to_a.should == ["That distributor or order cycle can't supply all the products in your cart. Please choose another."]
       end
 
-      it "empties the order if override is true" do
-        op.stub(:distribution_can_supply_products_in_cart).and_return true
-        order.stub(:with_lock).and_yield
-        order.should_receive(:empty!)
-        op.populate(params, true)
-      end
-
       it "locks the order" do
         op.stub(:distribution_can_supply_products_in_cart).and_return(true)
         order.should_receive(:with_lock)
@@ -37,9 +68,9 @@ module Spree
 
       it "attempts cart add with max_quantity" do
         op.stub(:distribution_can_supply_products_in_cart).and_return true
-        order.should_receive(:empty!)
         params = {variants: {"1" => {quantity: 1, max_quantity: 2}}}
         order.stub(:with_lock).and_yield
+        op.stub(:varies_from_cart) { true }
         op.should_receive(:attempt_cart_add).with("1", 1, 2).and_return true
         op.populate(params, true)
       end