Subpartitioning: Adds support for Prefix Partition Key searches for sub partitioned containers

Microsoft.Azure.Cosmos/src/FeedRange/FeedRange.cs

@@ -5,6 +5,8 @@
 namespace Microsoft.Azure.Cosmos
 {
     using System;
+    using System.Threading;
+    using System.Threading.Tasks;
 
     /// <summary>
     /// Represents a unit of feed consumption that can be used as unit of parallelism.
@@ -43,5 +45,32 @@ public static FeedRange FromPartitionKey(PartitionKey partitionKey)
         {
             return new FeedRangePartitionKey(partitionKey);
         }
+
+#if PREVIEW
+        /// <summary>
+        /// Creates a partition key or effective partition key feed range.
+        /// </summary>
+        /// <param name="container">The container.</param>
+        /// <param name="partitionKey">The partition key.</param>
+        /// <param name="cancellationToken">The cancellation token.</param>
+        /// <returns>A <see cref="Task{TResult}"/> representing the result of the asynchronous operation.</returns>
+        public
+#else
+        internal
+#endif
+            async static Task<FeedRange> CreateFromPartitionKeyAsync(
+            Container container,
+            PartitionKey partitionKey,
+            CancellationToken cancellationToken = default)
+        {
+            ContainerProperties containerProperties = await container.ReadContainerAsync(cancellationToken: cancellationToken).ConfigureAwait(false);
+            Documents.PartitionKeyDefinition partitionKeyDefinition = containerProperties.PartitionKey;
+
+            return FeedRangeEpk.IsPrefixPartitionKey(partitionKey: partitionKey, partitionKeyDefinition: partitionKeyDefinition) switch
+            {
+                true => FeedRangeEpk.CreateFromPartitionKey(partitionKey: partitionKey, partitionKeyDefinition: partitionKeyDefinition),
+                false => FeedRangePartitionKey.CreateFromPartitionKey(partitionKey),
+            };
+        }
     }
 }

Microsoft.Azure.Cosmos/src/FeedRange/FeedRanges/FeedRangeEpk.cs

@@ -109,5 +109,19 @@ public override int GetHashCode()
                 ^ this.Range.IsMinInclusive.GetHashCode()
                 ^ this.Range.IsMaxInclusive.GetHashCode();
         }
+
+        internal static FeedRangeEpk CreateFromPartitionKey(
+            Documents.PartitionKeyDefinition partitionKeyDefinition,
+            PartitionKey partitionKey)
+        {
+            return new FeedRangeEpk(partitionKey.InternalKey.GetEPKRangeForPrefixPartitionKey(partitionKeyDefinition));
+        }
+
+        internal static bool IsPrefixPartitionKey(
+            PartitionKey partitionKey,
+            Documents.PartitionKeyDefinition partitionKeyDefinition)
+        {
+            return !(partitionKey.InternalKey?.Components?.Count >= partitionKeyDefinition.Paths?.Count);
+        }
     }
 }

Microsoft.Azure.Cosmos/src/FeedRange/FeedRanges/FeedRangePartitionKey.cs

@@ -81,5 +81,15 @@ internal override TResult Accept<TResult>(IFeedRangeTransformer<TResult> transfo
         {
             return transformer.Visit(this);
         }
+
+        /// <summary>
+        /// Creates a feed range that span only a single <see cref="PartitionKey"/> value.
+        /// </summary>
+        /// <param name="partitionKey">The partition key value to create a feed range from.</param>
+        /// <returns>The feed range that spans the partition.</returns>
+        internal static FeedRange CreateFromPartitionKey(PartitionKey partitionKey)
+        {
+            return new FeedRangePartitionKey(partitionKey);
+        }
     }
 }

Microsoft.Azure.Cosmos/src/Microsoft.Azure.Cosmos.csproj

@@ -174,7 +174,7 @@
 	<PropertyGroup>
 		<DefineConstants Condition=" '$(SignAssembly)' == 'true' ">$(DefineConstants);SignAssembly</DefineConstants>
 		<DefineConstants Condition=" '$(DelaySign)' == 'true' ">$(DefineConstants);DelaySignKeys</DefineConstants>
-		<DefineConstants>$(DefineConstants);DOCDBCLIENT;COSMOSCLIENT;NETSTANDARD20</DefineConstants>
+		<DefineConstants>$(DefineConstants);DOCDBCLIENT;COSMOSCLIENT;NETSTANDARD20;PREVIEW</DefineConstants>
 	</PropertyGroup>
 
 </Project>