Filter checkins by date in Mongo instead of in Ruby

backend/app/controllers/api/v1/checkins_controller.rb

@@ -7,9 +7,10 @@ def index
         if date.blank? && params.require(:page)
           render json: current_user.checkins.where(:note.nin => [nil, ""]).order_by(date: :desc).page(params[:page]).per(10)
         else
-          render json: current_user.checkins.includes([:harvey_bradshaw_index, :promotion_rate, :conditions, :symptoms, :treatments]).select { |x|
-            x.date.to_date == Date.parse(date)
-          }
+          day = Date.parse(date)
+          checkins = current_user.checkins.by_date(day.beginning_of_day, day.end_of_day)
+          # to_a so the criteria is loaded and eager loaded once, not once per serializer pass
+          render json: checkins.includes([:harvey_bradshaw_index, :promotion_rate, :conditions, :symptoms, :treatments]).to_a
         end
       end
 

backend/spec/controllers/api/v1/checkins_controller_spec.rb

@@ -22,6 +22,15 @@
         returned_checkin = response_body[:checkins][0]
         expect(Date.parse(returned_checkin[:date])).to eq Date.parse(date)
       end
+
+      it "filters by date in the database instead of loading every checkin" do
+        commands = capture_mongo_commands { get :index, params: {date: date} }
+
+        checkin_finds = commands.select { |command| command.command["find"] == "checkins" }
+
+        expect(checkin_finds.size).to eq 1
+        expect(checkin_finds.first.command["filter"]["date"].keys).to match_array ["$gte", "$lte"]
+      end
     end
     context "when checkin doesn't exist for the passed date" do
       it "returns no results" do

backend/spec/support/mongo_commands.rb

@@ -0,0 +1,39 @@
+# Captures the commands the Mongo driver sends while a block runs, so specs can
+# assert that filtering happens in the database rather than in Ruby.
+module MongoCommands
+  class Subscriber
+    attr_reader :commands
+
+    def initialize
+      @commands = []
+    end
+
+    def started(event)
+      @commands << event
+    end
+
+    def succeeded(event)
+    end
+
+    def failed(event)
+    end
+  end
+
+  def capture_mongo_commands
+    subscriber = Subscriber.new
+    client = Mongoid.default_client
+    client.subscribe(Mongo::Monitoring::COMMAND, subscriber)
+
+    begin
+      yield
+    ensure
+      client.unsubscribe(Mongo::Monitoring::COMMAND, subscriber)
+    end
+
+    subscriber.commands
+  end
+end
+
+RSpec.configure do |config|
+  config.include MongoCommands, type: :controller
+end