Stop document context manager from saving if an error is raised.

Author: smithsz

CHANGES.md

@@ -1,7 +1,9 @@
 # Unreleased
 
-- [IMPROVED] Updated `Getting started` section with a `get_query_result` example. 
+- [FIXED] Bug where document context manager performed remote save despite
+  uncaught exceptions being raised inside `with` block.
 - [FIXED] Fixed parameter type of `selector` in docstring.
+- [IMPROVED] Updated `Getting started` section with a `get_query_result` example.
 
 # 2.11.0 (2019-01-21)
 

src/cloudant/document.py

@@ -341,12 +341,13 @@ def __enter__(self):
 
         return self
 
-    def __exit__(self, *args):
+    def __exit__(self, exc_type, exc_value, traceback):
         """
-        Support context like editing of document fields.  Handles context exit
-        logic.  Executes a Document.save() upon exit.
+        Support context like editing of document fields. Handles context exit
+        logic. Executes a `Document.save()` upon exit if no exception occurred.
         """
-        self.save()
+        if exc_type is None:
+            self.save()
 
     def __setitem__(self, key, value):
         """

tests/unit/document_tests.py

@@ -622,6 +622,47 @@ def test_document_context_manager_no_doc_id(self):
         self.assertTrue(doc['_rev'].startswith('1-'))
         self.assertEqual(self.db['julia006'], doc)
 
+    def test_document_context_manager_creation_failure_on_error(self):
+        """
+        Test that the document context manager skips document creation if there
+        is an error.
+        """
+        with self.assertRaises(ZeroDivisionError), Document(self.db, 'julia006') as doc:
+            doc['name'] = 'julia'
+            doc['age'] = 6
+            raise ZeroDivisionError()
+
+        doc = Document(self.db, 'julia006')
+        try:
+            doc.fetch()
+        except requests.HTTPError as err:
+            self.assertEqual(err.response.status_code, 404)
+        else:
+            self.fail('Above statement should raise a HTTPError.')
+
+    def test_document_context_manager_update_failure_on_error(self):
+        """
+        Test that the document context manager skips document update if there
+        is an error.
+        """
+        # Create the document.
+        doc = Document(self.db, 'julia006')
+        doc['name'] = 'julia'
+        doc['age'] = 6
+        doc.save()
+
+        # Make a document update and then raise an error.
+        with self.assertRaises(ZeroDivisionError), Document(self.db, 'julia006') as doc:
+            doc['age'] = 7
+            raise ZeroDivisionError()
+
+        # Assert the change persists locally.
+        self.assertEqual(doc['age'], 7)
+
+        # Assert the document has not been saved to remote server.
+        self.assertTrue(doc['_rev'].startswith('1-'))
+        self.assertEqual(self.db['julia006']['age'], 6)
+
     def test_document_context_manager_doc_create(self):
         """
         Test that the document context manager will create a doc if it does