do not update modified_by for system fields

awx/main/models/base.py

@@ -256,6 +256,7 @@ class PrimordialModel(CreatedModifiedModel):
 
     def save(self, *args, **kwargs):
         update_fields = kwargs.get('update_fields', [])
+        fields_are_specified = bool(update_fields)
         user = get_current_user()
         if user and not user.id:
             user = None
@@ -263,9 +264,14 @@ class PrimordialModel(CreatedModifiedModel):
             self.created_by = user
             if 'created_by' not in update_fields:
                 update_fields.append('created_by')
-        self.modified_by = user
-        if 'modified_by' not in update_fields:
-            update_fields.append('modified_by')
+        # Update modified_by if not called with update_fields, or if any
+        # editable fields are present in update_fields
+        if (
+                (not fields_are_specified) or
+                any(getattr(self._meta.get_field(name), 'editable', True) for name in update_fields)):
+            self.modified_by = user
+            if 'modified_by' not in update_fields:
+                update_fields.append('modified_by')
         super(PrimordialModel, self).save(*args, **kwargs)
 
     def clean_description(self):

awx/main/tests/functional/models/test_job.py

@@ -1,6 +1,7 @@
 import pytest
 
 from awx.main.models import JobTemplate, Job
+from crum import impersonate
 
 
 @pytest.mark.django_db
@@ -49,3 +50,18 @@ def test_awx_custom_virtualenv_without_jt(project):
 
     job = Job.objects.get(pk=job.id)
     assert job.ansible_virtualenv_path == '/venv/fancy-proj'
+
+
+@pytest.mark.django_db
+def test_update_parent_instance(job_template, alice):
+    # jobs are launched as a particular user, user not saved as modified_by
+    with impersonate(alice):
+        assert job_template.current_job is None
+        assert job_template.status == 'never updated'
+        assert job_template.modified_by is None
+        job = job_template.jobs.create(status='new')
+        job.status = 'pending'
+        job.save()
+        assert job_template.current_job == job
+        assert job_template.status == 'pending'
+        assert job_template.modified_by is None