Represent FileFields as their file path+name in the captured state

This means a FileField is only 'dirty' if the file path/name changes.
This fixes FileField performance regression caused by Django 3.1

ChangeLog.rst

@@ -6,6 +6,10 @@ ChangeLog
 unreleased
 ------
 
+*Changed:*
+    - Only look at the file name when determining if FileFields are dirty.
+    - Return only the file name in :code:`get_dirty_fields()` for FileFields.
+
 
 .. _v1.8.2:
 

src/dirtyfields/dirtyfields.py

@@ -1,6 +1,7 @@
 from copy import deepcopy
 
 from django.core.exceptions import ValidationError
+from django.core.files import File
 from django.db.models.expressions import BaseExpression
 from django.db.models.expressions import Combinable
 from django.db.models.signals import post_save, m2m_changed
@@ -79,6 +80,11 @@ def _as_dict(self, check_relationship, include_primary_key=True):
 
             field_value = getattr(self, field.attname)
 
+            if isinstance(field_value, File):
+                # Uses the name for files due to a perfomance regression caused by Django 3.1.
+                # For more info see: https://github.com/romgar/django-dirtyfields/issues/165
+                field_value = field_value.name
+
             # If current field value is an expression, we are not evaluating it
             if isinstance(field_value, (BaseExpression, Combinable)):
                 continue

tests/test_core.py

@@ -10,7 +10,6 @@
                      ModelWithOneToOneFieldTest,
                      SubclassModelTest, ModelWithDecimalFieldTest,
                      FileFieldModel, OrdinaryModelTest, OrdinaryWithDirtyFieldsProxy)
-from .utils import FakeFieldFile
 
 
 def test_version_numbers():
@@ -219,19 +218,19 @@ def test_refresh_from_db_no_fields():
 def test_file_fields_content_file():
     tm = FileFieldModel()
     # field is dirty because model is unsaved
-    assert tm.get_dirty_fields() == {"file1": FakeFieldFile("")}
+    assert tm.get_dirty_fields() == {"file1": ""}
     tm.save()
     assert tm.get_dirty_fields() == {}
 
     # set file makes field dirty
     tm.file1.save("test-file-1.txt", ContentFile(b"Test file content 1"), save=False)
-    assert tm.get_dirty_fields() == {"file1": FakeFieldFile("")}
+    assert tm.get_dirty_fields() == {"file1": ""}
     tm.save()
     assert tm.get_dirty_fields() == {}
 
     # change file makes field dirty
     tm.file1.save("test-file-2.txt", ContentFile(b"Test file content 2"), save=False)
-    assert tm.get_dirty_fields() == {"file1": FakeFieldFile("file1/test-file-1.txt")}
+    assert tm.get_dirty_fields() == {"file1": "file1/test-file-1.txt"}
     tm.save()
     assert tm.get_dirty_fields() == {}
 
@@ -240,21 +239,21 @@ def test_file_fields_content_file():
 def test_file_fields_real_file():
     tm = FileFieldModel()
     # field is dirty because model is unsaved
-    assert tm.get_dirty_fields() == {"file1": FakeFieldFile("")}
+    assert tm.get_dirty_fields() == {"file1": ""}
     tm.save()
     assert tm.get_dirty_fields() == {}
 
     # set file makes field dirty
     with open(join(dirname(__file__), "files", "foo.txt"), "rb") as f:
         tm.file1.save("test-file-3.txt", File(f), save=False)
-    assert tm.get_dirty_fields() == {"file1": FakeFieldFile("")}
+    assert tm.get_dirty_fields() == {"file1": ""}
     tm.save()
     assert tm.get_dirty_fields() == {}
 
     # change file makes field dirty
     with open(join(dirname(__file__), "files", "bar.txt"), "rb") as f:
         tm.file1.save("test-file-4.txt", File(f), save=False)
-    assert tm.get_dirty_fields() == {"file1": FakeFieldFile("file1/test-file-3.txt")}
+    assert tm.get_dirty_fields() == {"file1": "file1/test-file-3.txt"}
     tm.save()
     assert tm.get_dirty_fields() == {}
 

tests/utils.py

@@ -1,5 +1,4 @@
 import re
-from collections import namedtuple
 
 from django.conf import settings
 from django.db import connection
@@ -63,7 +62,3 @@ def is_postgresql_env_with_jsonb_field():
         PG_VERSION = 0
 
     return PG_VERSION >= 90400
-
-
-# Will compare equal with a django `FieldFile` instance in tests.
-FakeFieldFile = namedtuple("FakeFieldFile", ["name"])