Support empty new models. #11

Author: ses4j

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Added
 
+-   Added support for manually specifying model to act on if new_models is empty. #11.
 -   Added exclude_fields argument. Issue #15, pull request #16 from [@VKFisher](https://github.com/VKFisher).
 
 ## [3.0.1] - 2020-08-05

README.md

@@ -79,6 +79,7 @@ Combine bulk create, update, and delete. Make the DB match a set of in-memory ob
 -   `skip_creates`: (optional) If truthy, will not perform any object creations needed to fully sync. Defaults to not skip.
 -   `skip_updates`: (optional) If truthy, will not perform any object updates needed to fully sync. Defaults to not skip.
 -   `skip_deletes`: (optional) If truthy, will not perform any object deletions needed to fully sync. Defaults to not skip.
+-   `db_class`: (optional) Model class to operate on. If new_models always contains at least one object, this can be set automatically so is optional.
 
 -   Returns a dict:
     ```

bulk_sync/__init__.py

@@ -17,6 +17,7 @@ def bulk_sync(
     skip_creates=False,
     skip_updates=False,
     skip_deletes=False,
+    db_class=None,
 ):
     """ Combine bulk create, update, and delete.  Make the DB match a set of in-memory objects.
 
@@ -34,8 +35,23 @@ def bulk_sync(
     `skip_creates`: If truthy, will not perform any object creations needed to fully sync. Defaults to not skip.
     `skip_updates`: If truthy, will not perform any object updates needed to fully sync. Defaults to not skip.
     `skip_deletes`: If truthy, will not perform any object deletions needed to fully sync. Defaults to not skip.
+    `db_class`: (optional) Model class to operate on. If new_models always contains at least one object, this can
+            be set automatically so is optional.
     """
-    db_class = new_models[0].__class__
+
+    if db_class is None:
+        try:
+            db_class = new_models[0].__class__
+        except IndexError:
+            try:
+                db_class = new_models.model
+            except AttributeError:
+                db_class = None
+
+    if db_class is None:
+        raise RuntimeError(
+            "Unable to identify model to sync. Need to provide at least one object in `new_models`, provide `db_class`, or set `new_models` with a queryset like `db_class.objects.none()`."
+        )
 
     if fields is None:
         # Get a list of fields that aren't PKs and aren't editable (e.g. auto_add_now) for bulk_update

tests/tests.py

@@ -210,6 +210,15 @@ def test_skip_updates(self):
         self.assertEqual(1, ret["stats"]["created"])
         self.assertEqual(1, ret["stats"]["deleted"])
 
+    def test_empty_new_models_class_detection_works(self):
+        c1 = Company.objects.create(name="My Company LLC")
+
+        with self.assertRaises(RuntimeError):
+            ret = bulk_sync(new_models=[], filters=None, key_fields=("name",))
+
+        ret = bulk_sync(new_models=[], filters=None, key_fields=("name",), db_class=Employee)
+        ret = bulk_sync(new_models=Employee.objects.none(), filters=None, key_fields=("name",))
+
 
 class BulkCompareTests(TestCase):
     """ Test `bulk_compare` method """