Fix Dataset.get when there are transforms in the dataset (#45)

* Fix dataset get when there are transforms

* Extend test

* Update changelog

* Help linter

CHANGELOG.md

@@ -94,6 +94,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   (<https://github.com/cvat-ai/datumaro/pull/34>)
 - Incorrect computation of binary mask bbox (missed 1 pixel of the size)
   (<https://github.com/cvat-ai/datumaro/pull/41>)
+- `Dataset.get()` could ignore existing transforms in the dataset
+  (<https://github.com/cvat-ai/datumaro/pull/45>)
 
 ### Security
 - TBD

datumaro/components/dataset.py

@@ -419,8 +419,9 @@ def _update_status(item_id, new_status: ItemStatus):
         source = self._source or DatasetItemStorageDatasetView(
             self._storage, categories=self._categories, media_type=media_type
         )
-        transform = None
 
+        transform = None
+        old_ids = None
         if self._transforms:
             transform = _StackedTransform(source, self._transforms)
             if transform.is_local:
@@ -588,7 +589,7 @@ def get(self, id, subset=None) -> Optional[DatasetItem]:
 
         item = self._storage.get(id, subset)
         if item is None and not self.is_cache_initialized():
-            if self._source.get.__func__ == Extractor.get:
+            if self._source.get.__func__ == Extractor.get or self._transforms:
                 # can be improved if IDataset is ABC
                 self.init_cache()
                 item = self._storage.get(id, subset)

tests/test_dataset.py

@@ -1267,6 +1267,77 @@ def __iter__(self):
 
         self.assertEqual(iter_called, 2)
 
+    @mark_requirement(Requirements.DATUM_GENERAL_REQ)
+    def test_can_get_item_after_local_transforms(self):
+        iter_called = 0
+
+        class TestExtractor(Extractor):
+            def __iter__(self):
+                nonlocal iter_called
+                iter_called += 1
+                yield from [
+                    DatasetItem(1),
+                    DatasetItem(2),
+                    DatasetItem(3),
+                    DatasetItem(4),
+                ]
+
+        dataset = Dataset.from_extractors(TestExtractor())
+
+        class TestTransform(ItemTransform):
+            def transform_item(self, item):
+                return self.wrap_item(item, id=int(item.id) + 1)
+
+        dataset.transform(TestTransform)
+        dataset.transform(TestTransform)
+
+        self.assertEqual(iter_called, 0)
+
+        self.assertIsNone(dataset.get(1))
+        self.assertIsNone(dataset.get(2))
+        self.assertIsNotNone(dataset.get(3))
+        self.assertIsNotNone(dataset.get(4))
+        self.assertIsNotNone(dataset.get(5))
+        self.assertIsNotNone(dataset.get(6))
+
+        self.assertEqual(iter_called, 1)
+
+    @mark_requirement(Requirements.DATUM_GENERAL_REQ)
+    def test_can_get_item_after_nonlocal_transforms(self):
+        iter_called = 0
+
+        class TestExtractor(Extractor):
+            def __iter__(self):
+                nonlocal iter_called
+                iter_called += 1
+                yield from [
+                    DatasetItem(1),
+                    DatasetItem(2),
+                    DatasetItem(3),
+                    DatasetItem(4),
+                ]
+
+        dataset = Dataset.from_extractors(TestExtractor())
+
+        class TestTransform(Transform):
+            def __iter__(self):
+                for item in self._extractor:
+                    yield self.wrap_item(item, id=int(item.id) + 1)
+
+        dataset.transform(TestTransform)
+        dataset.transform(TestTransform)
+
+        self.assertEqual(iter_called, 0)
+
+        self.assertIsNone(dataset.get(1))
+        self.assertIsNone(dataset.get(2))
+        self.assertIsNotNone(dataset.get(3))
+        self.assertIsNotNone(dataset.get(4))
+        self.assertIsNotNone(dataset.get(5))
+        self.assertIsNotNone(dataset.get(6))
+
+        self.assertEqual(iter_called, 2)
+
     @mark_requirement(Requirements.DATUM_GENERAL_REQ)
     def test_can_get_subsets_after_local_transforms(self):
         iter_called = 0