Fix issue pandas-dev#360

Author: bmoscon

CHANGES.md

@@ -2,6 +2,7 @@
 
 ### 1.43
   * Bugfix: #350 remove deprecated pandas calls
+  * Bugfix: #360 version incorrect in empty append in VersionStore
 
 ### 1.42 (2017-05-12)
   * Bugfix: #346 fixed daterange subsetting error on very large dateframes in version store

arctic/store/version_store.py

@@ -465,7 +465,7 @@ def append(self, symbol, data, metadata=None, prune_previous_version=True, upser
                                                    sort=[('version', pymongo.DESCENDING)])
 
         if len(data) == 0 and previous_version is not None:
-            return VersionedItem(symbol=symbol, library=self._arctic_lib.get_name(), version=previous_version,
+            return VersionedItem(symbol=symbol, library=self._arctic_lib.get_name(), version=previous_version['version'],
                                  metadata=version.pop('metadata', None), data=None)
 
         if upsert and previous_version is None:

tests/integration/store/test_version_store.py

@@ -274,8 +274,10 @@ def test_append_should_overwrite_after_delete(library):
 
 
 def test_append_empty_ts(library):
-    library.append(symbol, ts1, upsert=True)
-    library.append(symbol, pd.DataFrame(), upsert=True)
+    data = library.append(symbol, ts1, upsert=True)
+    assert(data.version == 1)
+    data = library.append(symbol, pd.DataFrame(), upsert=True)
+    assert(data.version == 1)
     assert len(library.read(symbol).data) == len(ts1)