Ensure only a single action for a document is added to a batch

sdk/search/Azure.Search.Documents/src/Batching/Publisher.cs

@@ -422,12 +422,14 @@ await SubmitBatchAsync(
             // Returns whether the batch is now full.
             bool FillBatchFromQueue(List<PublisherAction<T>> batch, Queue< PublisherAction<T>> queue)
             {
-                // TODO: Consider tracking the keys in the batch and requiring
-                // them to be unique to avoid error alignment problems
+                HashSet<string> documentIdentifiers = new HashSet<string>(StringComparer.Ordinal);
 
                 while (queue.Count > 0)
                 {
-                    if (batch.Count < BatchActionCount)
+                    // Stop filling the batch if we run into an action for a document that is already in the batch.
+                    // We want to keep the actions ordered and map any errors accurately to the documents,
+                    // so we need to split the batch on encountering an action for a previously queued document.
+                    if ((batch.Count < BatchActionCount) && documentIdentifiers.Add(queue.Peek().Key))
                     {
                         batch.Add(queue.Dequeue());
                     }

sdk/search/Azure.Search.Documents/tests/Batching/BatchingTests.cs

@@ -1031,6 +1031,65 @@ public async Task Behavior_BatchSize()
             Assert.AreEqual(5, client.Submissions.Count);
         }
 
+        [Test]
+        public async Task Behavior_SplitBatchByDocumentKey()
+        {
+            int numberOfDocuments = 5;
+
+            await using SearchResources resources = await SearchResources.CreateWithEmptyIndexAsync<SimpleDocument>(this);
+            BatchingSearchClient client = GetBatchingSearchClient(resources);
+
+            SimpleDocument[] data = new SimpleDocument[numberOfDocuments];
+            for (int i = 0; i < numberOfDocuments; i++)
+            {
+                data[i] = new SimpleDocument() { Id = $"{i}", Name = $"Document #{i}" };
+            }
+
+            // 'SimpleDocument' has 'Id' set as its key field.
+            // Set the Ids of 2 documents in the group to be the same.
+            // We expect the batch to be split at this index, even though the size of the set is smaller than the batch size.
+            data[3].Id = data[0].Id;
+
+            await using SearchIndexingBufferedSender<SimpleDocument> indexer =
+                client.CreateIndexingBufferedSender(
+                    new SearchIndexingBufferedSenderOptions<SimpleDocument>()
+                    {
+                        // Set the expected batch action count to be larger than the number of documents in the set.
+                        InitialBatchActionCount = numberOfDocuments + 1,
+                    });
+
+            // Throw from every handler
+            int sent = 0, completed = 0;
+            indexer.ActionSent += e =>
+            {
+                sent++;
+
+                // Batch will be split at the 4th document.
+                // So, 3 documents will be sent before any are submitted, but 3 submissions will be made before the last 2 are sent
+                Assert.AreEqual((sent <= 3) ? 0 : 3, completed);
+
+                throw new InvalidOperationException("ActionSentAsync: Should not be seen!");
+            };
+
+            indexer.ActionCompleted += e =>
+            {
+                completed++;
+
+                // Batch will be split at the 4th document.
+                // So, 3 documents will be submitted after 3 are sent, and the last 2 submissions will be made after all 5 are sent
+                Assert.AreEqual((completed <= 3) ? 3 : 5, sent);
+
+                throw new InvalidOperationException("ActionCompletedAsync: Should not be seen!");
+            };
+
+            AssertNoFailures(indexer);
+            await indexer.UploadDocumentsAsync(data);
+            await indexer.FlushAsync();
+
+            Assert.AreEqual(5, sent);
+            Assert.AreEqual(5, completed);
+        }
+
         [Test]
         [TestCase(409)]
         [TestCase(422)]