Fix support for default values when upserting

Fixes #20

Author: Photonios

psqlextra/manager.py

@@ -6,6 +6,7 @@
 from django.db import models, transaction
 from django.db.models.sql import UpdateQuery
 from django.db.models.sql.constants import CURSOR
+from django.db.models.fields import NOT_PROVIDED
 
 from . import signals
 from .compiler import (PostgresReturningUpdateCompiler,
@@ -323,10 +324,14 @@ def _get_upsert_fields(self, kwargs):
         update_fields = []
 
         for field in model_instance._meta.local_concrete_fields:
-            if field.name in kwargs or field.column in kwargs:
+            has_default = field.default != NOT_PROVIDED
+            if (field.name in kwargs or field.column in kwargs):
                 insert_fields.append(field)
                 update_fields.append(field)
                 continue
+            elif has_default:
+                insert_fields.append(field)
+                continue
 
             # special handling for 'pk' which always refers to
             # the primary key, so if we the user specifies `pk`

tests/test_on_conflict.py

@@ -333,3 +333,57 @@ def test_on_conflict_pk_conflict_target(conflict_action):
     assert obj1.id == obj2.id
     assert obj1.id == 0
     assert obj2.id == 0
+
+
+def test_on_conflict_default_value():
+    """Tests whether setting a default for a field and
+    not specifying it explicitely when upserting properly
+    causes the default value to be used."""
+
+    model = get_fake_model({
+        'title': models.CharField(max_length=255, default='great')
+    })
+
+    obj1 = (
+        model.objects
+        .on_conflict(['id'], ConflictAction.UPDATE)
+        .insert_and_get(id=0)
+    )
+
+    assert obj1.title == 'great'
+
+    obj2 = (
+        model.objects
+        .on_conflict(['id'], ConflictAction.UPDATE)
+        .insert_and_get(id=0)
+    )
+
+    assert obj1.id == obj2.id
+    assert obj2.title == 'great'
+
+
+def test_on_conflict_default_value_no_overwrite():
+    """Tests whether setting a default for a field, inserting
+    a non-default value and then trying to update it without
+    specifying that field doesn't result in it being overwritten."""
+
+    model = get_fake_model({
+        'title': models.CharField(max_length=255, default='great')
+    })
+
+    obj1 = (
+        model.objects
+        .on_conflict(['id'], ConflictAction.UPDATE)
+        .insert_and_get(id=0, title='mytitle')
+    )
+
+    assert obj1.title == 'mytitle'
+
+    obj2 = (
+        model.objects
+        .on_conflict(['id'], ConflictAction.UPDATE)
+        .insert_and_get(id=0)
+    )
+
+    assert obj1.id == obj2.id
+    assert obj2.title == 'mytitle'