Improve effiency of OrderCycle.earliest_closing_times

app/models/order_cycle.rb

@@ -154,9 +154,8 @@ def self.earliest_closing_times
         joins(:order_cycle).
         merge(OrderCycle.active).
         group('exchanges.receiver_id').
-        select("exchanges.receiver_id AS receiver_id,
-                MIN(order_cycles.orders_close_at) AS earliest_close_at").
-        map { |ex| [ex.receiver_id, ex.earliest_close_at.to_time] }
+        pluck(Arel.sql("exchanges.receiver_id AS receiver_id"),
+              Arel.sql("MIN(order_cycles.orders_close_at) AS earliest_close_at"))
     ]
   end
 

app/serializers/api/uncached_enterprise_serializer.rb

@@ -7,7 +7,7 @@ class UncachedEnterpriseSerializer < ActiveModel::Serializer
     attributes :orders_close_at, :active
 
     def orders_close_at
-      options[:data].earliest_closing_times[object.id]
+      options[:data].earliest_closing_times[object.id]&.to_time
     end
 
     def active

spec/serializers/api/uncached_enterprise_serializer_spec.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Api::UncachedEnterpriseSerializer do
+  let(:serializer) {
+    described_class.new enterprise, { data: OpenFoodNetwork::EnterpriseInjectionData.new }
+  }
+  let(:enterprise) { create :enterprise }
+
+  before do
+    allow_any_instance_of(OpenFoodNetwork::EnterpriseInjectionData).to(
+      receive(:earliest_closing_times).
+        and_return(data)
+    )
+  end
+
+  describe '#orders_close_at' do
+    context "for an enterprise with an active order cycle" do
+      let(:order_cycle) { create :open_order_cycle, coordinator: enterprise }
+      let(:data) { { enterprise.id => order_cycle.orders_close_at } }
+
+      it "returns a closing time for an enterprise" do
+        expect(serializer.orders_close_at).to eq order_cycle.orders_close_at
+      end
+    end
+
+    context "for an enterprise without an active order cycle" do
+      let(:data) { {} }
+
+      it "returns nil for an enterprise without a closing time" do
+        expect(serializer.orders_close_at).to be_nil
+      end
+    end
+  end
+end