Improve performance for device query

Currently, device metadata was stored in two place - DocumentDB (for command, telemetries, etc.) and IoT Hub (for twin). We must try to merge those two data source for each query. In previous code, we query Document DB separately for each devices we retrieved from the IoT Hub. It may cause redundant initializing effort.

In this code change, we use one single query for all the devices to improve the performance. Furthermore, we are going to delay the query on Document DB until the result was paginated. It will bring some benefit for pagination case.

DeviceAdministration/Infrastructure/Infrastructure.csproj

@@ -72,6 +72,7 @@
       <HintPath>..\..\packages\Microsoft.Azure.Devices.Client.1.0.16\lib\net45\Microsoft.Azure.Devices.Client.dll</HintPath>
       <Private>True</Private>
     </Reference>
+    <Reference Include="Microsoft.Azure.Documents.Client, Version=1.9.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL" />
     <Reference Include="Microsoft.Data.Edm, Version=5.6.4.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
       <HintPath>..\..\packages\Microsoft.Data.Edm.5.6.4\lib\net40\Microsoft.Data.Edm.dll</HintPath>
       <Private>True</Private>

DeviceAdministration/Infrastructure/Repository/DeviceRegistryRepository.cs

@@ -12,7 +12,7 @@ namespace Microsoft.Azure.Devices.Applications.RemoteMonitoring.DeviceAdmin.Infr
 {
     public class DeviceRegistryRepository : IDeviceRegistryCrudRepository, IDeviceRegistryListRepository
     {
-        private readonly IDocumentDBClient<DeviceModel> _documentClient;
+        protected readonly IDocumentDBClient<DeviceModel> _documentClient;
 
         public DeviceRegistryRepository(IDocumentDBClient<DeviceModel> documentClient)
         {

DeviceAdministration/Infrastructure/Repository/DeviceRegistryRepositoryWithIoTHubDM.cs

@@ -71,27 +71,26 @@ namespace Microsoft.Azure.Devices.Applications.RemoteMonitoring.DeviceAdmin.Infr
 
         public override async Task<DeviceListQueryResult> GetDeviceList(DeviceListQuery query)
         {
+            // Kick-off DocDB query initializing
+            var queryTask = this._documentClient.QueryAsync();
+
             // Considering all the device properties was copied to IoT Hub twin as tag or
             // reported property, we will only query on the IoT Hub twins. The DocumentDB
             // will not be touched.
-            var twins = await this._deviceManager.QueryDevicesAsync(query);
-
-            var tasks = twins.Select(async twin =>
-            {
-                var device = await base.GetDeviceAsync(twin.DeviceId);
-                device.Twin = twin;
-                return device;
-            });
-
-            var filteredDevices = await Task.WhenAll(tasks);
+            var filteredDevices = await this._deviceManager.QueryDevicesAsync(query);
 
             var sortedDevices = this.SortDeviceList(filteredDevices.AsQueryable(), query.SortColumn, query.SortOrder);
 
             var pagedDeviceList = sortedDevices.Skip(query.Skip).Take(query.Take).ToList();
 
+            // Query on DocDB for traditional device properties, commands and so on
+            var deviceIds = pagedDeviceList.Select(twin => twin.DeviceId);
+            var deviceModels = (await queryTask).Where(x => deviceIds.Contains(x.DeviceProperties.DeviceID)).ToList();
+            deviceModels.ForEach(d => d.Twin = filteredDevices.Single(t => t.DeviceId == d.DeviceProperties.DeviceID));
+
             return new DeviceListQueryResult
             {
-                Results = pagedDeviceList,
+                Results = deviceModels,
                 TotalDeviceCount = (int)await this._deviceManager.GetDeviceCountAsync(),
                 TotalFilteredCount = filteredDevices.Count()
             };
@@ -107,7 +106,7 @@ namespace Microsoft.Azure.Devices.Applications.RemoteMonitoring.DeviceAdmin.Infr
             await this._deviceManager.UpdateTwinAsync(deviceId, twin);
         }
 
-        private IQueryable<DeviceModel> SortDeviceList(IQueryable<DeviceModel> deviceList, string sortColumn, QuerySortOrder sortOrder)
+        private IQueryable<Twin> SortDeviceList(IQueryable<Twin> deviceList, string sortColumn, QuerySortOrder sortOrder)
         {
             // if a sort column was not provided then return the full device list in its original sort
             if (string.IsNullOrWhiteSpace(sortColumn))
@@ -115,7 +114,7 @@ namespace Microsoft.Azure.Devices.Applications.RemoteMonitoring.DeviceAdmin.Infr
                 return deviceList;
             }
 
-            Func<DeviceModel, dynamic> keySelector = item => item.Twin.Get(sortColumn);
+            Func<Twin, dynamic> keySelector = twin => twin.Get(sortColumn);
 
             if (sortOrder == QuerySortOrder.Ascending)
             {