Complain if we try to export disassembled dataset

python/lsst/daf/butler/datastores/posixDatastore.py

@@ -331,9 +331,13 @@ def export(self, refs: Iterable[DatasetRef], *,
                directory: Optional[str] = None, transfer: Optional[str] = None) -> Iterable[FileDataset]:
         # Docstring inherited from Datastore.export.
         for ref in refs:
-            location, storedFileInfo = self._get_dataset_location_info(ref)
-            if location is None:
+            fileLocations = self._get_dataset_locations_info(ref)
+            if not fileLocations:
                 raise FileNotFoundError(f"Could not retrieve dataset {ref}.")
+            # For now we can not export disassembled datasets
+            if len(fileLocations) > 1:
+                raise NotImplementedError(f"Can not export disassembled datasets such as {ref}")
+            location, storedFileInfo = fileLocations[0]
             if transfer is None:
                 # TODO: do we also need to return the readStorageClass somehow?
                 yield FileDataset(refs=[ref], path=location.pathInStore, formatter=storedFileInfo.formatter)

tests/test_butler.py

@@ -832,6 +832,15 @@ def testPutTemplates(self):
     def testImportExport(self):
         # Run put/get tests just to create and populate a repo.
         storageClass = self.storageClassFactory.getStorageClass("StructuredDataNoComponents")
+        self.runImportExportTest(storageClass)
+
+    @unittest.expectedFailure
+    def testImportExportVirtualComposite(self):
+        # Run put/get tests just to create and populate a repo.
+        storageClass = self.storageClassFactory.getStorageClass("StructuredComposite")
+        self.runImportExportTest(storageClass)
+
+    def runImportExportTest(self, storageClass):
         exportButler = self.runPutGetTest(storageClass, "test_metric")
         # Test that the repo actually has at least one dataset.
         datasets = list(exportButler.registry.queryDatasets(..., collections=...))