fix: Dynamodb drops missing entities when batching

sdk/python/feast/infra/online_stores/dynamodb.py

@@ -221,6 +221,9 @@ def online_read(
         entity_ids_iter = iter(entity_ids)
         while True:
             batch = list(itertools.islice(entity_ids_iter, batch_size))
+            batch_result: List[
+                Tuple[Optional[datetime], Optional[Dict[str, ValueProto]]]
+            ] = []
             # No more items to insert
             if len(batch) == 0:
                 break
@@ -243,20 +246,23 @@ def online_read(
                 for tbl_res in table_responses:
                     entity_id = tbl_res["entity_id"]
                     while entity_id != batch[entity_idx]:
-                        result.append((None, None))
+                        batch_result.append((None, None))
                         entity_idx += 1
                     res = {}
                     for feature_name, value_bin in tbl_res["values"].items():
                         val = ValueProto()
                         val.ParseFromString(value_bin.value)
                         res[feature_name] = val
-                    result.append((datetime.fromisoformat(tbl_res["event_ts"]), res))
+                    batch_result.append(
+                        (datetime.fromisoformat(tbl_res["event_ts"]), res)
+                    )
                     entity_idx += 1
 
             # Not all entities in a batch may have responses
             # Pad with remaining values in batch that were not found
-            batch_size_nones = ((None, None),) * (len(batch) - len(result))
-            result.extend(batch_size_nones)
+            batch_size_nones = ((None, None),) * (len(batch) - len(batch_result))
+            batch_result.extend(batch_size_nones)
+            result.extend(batch_result)
         return result
 
     def _get_dynamodb_client(self, region: str, endpoint_url: Optional[str] = None):

sdk/python/tests/unit/infra/online_store/test_dynamodb_online_store.py

@@ -318,3 +318,42 @@ def test_write_batch_non_duplicates(repo_config, dynamodb_online_store):
     returned_items = response.get("Items", None)
     assert returned_items is not None
     assert len(returned_items) == len(data)
+
+
+@mock_dynamodb2
+def test_dynamodb_online_store_online_read_unknown_entity_end_of_batch(
+    repo_config, dynamodb_online_store
+):
+    """
+    Test DynamoDBOnlineStore online_read method with unknown entities at
+    the end of the batch.
+    """
+    batch_size = repo_config.online_store.batch_size
+    n_samples = batch_size
+    _create_test_table(PROJECT, f"{TABLE_NAME}_unknown_entity_{n_samples}", REGION)
+    data = _create_n_customer_test_samples(n=n_samples)
+    _insert_data_test_table(
+        data, PROJECT, f"{TABLE_NAME}_unknown_entity_{n_samples}", REGION
+    )
+
+    entity_keys, features, *rest = zip(*data)
+    entity_keys = list(entity_keys)
+    features = list(features)
+
+    # Append a nonsensical entity to search for as the only item in the 2nd batch
+    entity_keys.append(
+        EntityKeyProto(
+            join_keys=["customer"], entity_values=[ValueProto(string_val="12359")]
+        )
+    )
+    features.append(None)
+
+    returned_items = dynamodb_online_store.online_read(
+        config=repo_config,
+        table=MockFeatureView(name=f"{TABLE_NAME}_unknown_entity_{n_samples}"),
+        entity_keys=entity_keys,
+    )
+
+    # ensure the entity is not dropped
+    assert len(returned_items) == len(entity_keys)
+    assert returned_items[-1] == (None, None)