ORDER BY Undefined (#952)

* reproduced issue

* got tests to pass

* removed mixed type order by check

* updated changelog

Microsoft.Azure.Cosmos/src/Query/Core/OrderByItem.cs

@@ -45,7 +45,7 @@ public CosmosElement Item
             {
                 if (!this.cosmosObject.TryGetValue(ItemName, out CosmosElement cosmosElement))
                 {
-                    throw new InvalidOperationException($"Underlying object does not have an 'item' field.");
+                    cosmosElement = null;
                 }
 
                 return cosmosElement;

Microsoft.Azure.Cosmos/src/Query/Core/OrderByQuery/OrderByConsumeComparer.cs

@@ -6,9 +6,6 @@ namespace Microsoft.Azure.Cosmos.Query.ParallelQuery
     using System;
     using System.Collections.Generic;
     using System.Diagnostics;
-    using System.Globalization;
-    using Microsoft.Azure.Cosmos.CosmosElements;
-    using RMResources = Documents.RMResources;
 
     /// <summary>
     /// For cross partition order by queries we serve documents from the partition
@@ -17,12 +14,6 @@ namespace Microsoft.Azure.Cosmos.Query.ParallelQuery
     /// </summary>
     internal sealed class OrderByConsumeComparer : IComparer<ItemProducerTree>
     {
-        /// <summary>
-        /// This flag used to determine whether we should support mixed type order by.
-        /// For testing purposes we might turn it on to test mixed type order by on index v2.
-        /// </summary>
-        public static bool AllowMixedTypeOrderByTestFlag = false;
-
         /// <summary>
         /// The sort orders for the query (1 for each order by in the query).
         /// Until composite indexing is released this will just be an array of length 1.
@@ -132,11 +123,6 @@ public int CompareOrderByItems(IList<OrderByItem> items1, IList<OrderByItem> ite
                 this.sortOrders.Count == items1.Count,
                 "SortOrders must match size of order-by items.");
 
-            if (!AllowMixedTypeOrderByTestFlag)
-            {
-                this.CheckTypeMatching(items1, items2);
-            }
-
             for (int i = 0; i < this.sortOrders.Count; ++i)
             {
                 int cmp = ItemComparer.Instance.Compare(
@@ -151,39 +137,5 @@ public int CompareOrderByItems(IList<OrderByItem> items1, IList<OrderByItem> ite
 
             return 0;
         }
-
-        /// <summary>
-        /// With index V1 collections we have the check the types of the items since it is impossible to support mixed typed order by for V1 collections.
-        /// The reason for this is, since V1 does not order types.
-        /// The only constraint is that all the numbers will be sorted with respect to each other and same for the strings, but strings and numbers might get interleaved.
-        /// Take the following example:
-        /// Partition 1: "A", 1, "B", 2
-        /// Partition 2: 42, "Z", 0x5F3759DF
-        /// Step 1: Compare "A" to 42 and WLOG 42 comes first
-        /// Step 2: Compare "A" to "Z" and "A" comes first
-        /// Step 3: Compare "Z" to 1 and WLOG 1 comes first
-        /// Whoops: We have 42, "A", 1 and 1 should come before 42.
-        /// </summary>
-        /// <param name="items1">The items relevant to the sort for the first partition.</param>
-        /// <param name="items2">The items relevant to the sort for the second partition.</param>
-        private void CheckTypeMatching(IList<OrderByItem> items1, IList<OrderByItem> items2)
-        {
-            for (int i = 0; i < items1.Count; ++i)
-            {
-                CosmosElementType itemType1 = items1[i].Item.Type;
-                CosmosElementType itemType2 = items2[i].Item.Type;
-
-                if (itemType1 != itemType2)
-                {
-                    throw new NotSupportedException(
-                        string.Format(
-                            CultureInfo.InvariantCulture,
-                            RMResources.UnsupportedCrossPartitionOrderByQueryOnMixedTypes,
-                            itemType1,
-                            itemType2,
-                            items1[i]));
-                }
-            }
-        }
     }
 }