fix #115 correctly

Author: PetrDlouhy

README.rst

@@ -169,18 +169,33 @@ To exclude or disable file formats from the admin site, configure `IMPORT_EXPORT
 
         IMPORT_EXPORT_CELERY_EXCLUDED_FORMATS = ["csv", "xls"]
 
+
 Customizing File Storage Backend
 --------------------------------
 
-Define a custom storage backend by adding the `IMPORT_EXPORT_CELERY_STORAGE` to your Django settings STORAGES definition. For instance:
+**If you are using the new Django 4.2 STORAGES**:
+
+By default, `import_export_celery` uses Django `default` storage.
+To use your own storage, use the the `IMPORT_EXPORT_CELERY_STORAGE_ALIAS` variable in your Django settings and adding the STORAGES definition.
+For instance:
 
     ::
 
         STORAGES = {
-            "IMPORT_EXPORT_CELERY_STORAGE": {
+            "import_export_celery": {
                 "BACKEND": "storages.backends.s3boto3.S3Boto3Storage",
             },
         }
+        IMPORT_EXPORT_CELERY_STORAGE_ALIAS = 'import_export_celery'
+
+**DEPRECATED: If you are using old style storages**:
+
+Define a custom storage backend by adding the `IMPORT_EXPORT_CELERY_STORAGE` to your Django settings. For instance:
+
+    ::
+
+        IMPORT_EXPORT_CELERY_STORAGE = "storages.backends.s3boto3.S3Boto3Storage"
+
 
 Customizing Task Time Limits
 ----------------------------

example/project/settings.py

@@ -98,18 +98,6 @@
         },
     }
 
-STORAGES = {
-    "IMPORT_EXPORT_CELERY_STORAGE": {
-        "BACKEND": "django.core.files.storage.FileSystemStorage",
-    },
-    "staticfiles": {
-        "BACKEND": "django.core.files.storage.FileSystemStorage",
-    },
-    "default": {
-        "BACKEND": "django.core.files.storage.FileSystemStorage",
-    }
-}
-
 # Password validation
 # https://docs.djangoproject.com/en/1.10/ref/settings/#auth-password-validators
 

example/winners/tests/test_fields.py

@@ -0,0 +1,60 @@
+import django
+from django.test import TestCase, override_settings
+from django.conf import settings
+from django.core.files.storage import FileSystemStorage
+import unittest
+
+from import_export_celery.fields import lazy_initialize_storage_class
+
+
+class FooTestingStorage(FileSystemStorage):
+    pass
+
+
+class InitializeStorageClassTests(TestCase):
+
+    def test_default(self):
+        self.assertIsInstance(lazy_initialize_storage_class(), FileSystemStorage)
+
+    @unittest.skipUnless(django.VERSION < (5, 1), "Test only applicable for Django versions < 5.1")
+    @override_settings(
+        IMPORT_EXPORT_CELERY_STORAGE="winners.tests.test_fields.FooTestingStorage"
+    )
+    def test_old_style(self):
+        del settings.IMPORT_EXPORT_CELERY_STORAGE_ALIAS
+        del settings.STORAGES
+        self.assertIsInstance(lazy_initialize_storage_class(), FooTestingStorage)
+
+    @unittest.skipUnless((4, 2) <= django.VERSION, "Test only applicable for Django 4.2 and later")
+    @override_settings(
+        IMPORT_EXPORT_CELERY_STORAGE_ALIAS="test_import_export_celery",
+        STORAGES={
+            "test_import_export_celery": {
+                "BACKEND": "winners.tests.test_fields.FooTestingStorage",
+            },
+            "staticfiles": {
+                "BACKEND": "django.core.files.storage.FileSystemStorage",
+            },
+            "default": {
+                "BACKEND": "django.core.files.storage.FileSystemStorage",
+            }
+        }
+
+    )
+    def test_new_style(self):
+        self.assertIsInstance(lazy_initialize_storage_class(), FooTestingStorage)
+
+    @unittest.skipUnless((4, 2) <= django.VERSION, "Test only applicable for Django 4.2 and later")
+    @override_settings(
+        STORAGES={
+            "staticfiles": {
+                "BACKEND": "django.core.files.storage.FileSystemStorage",
+            },
+            "default": {
+                "BACKEND": "winners.tests.test_fields.FooTestingStorage",
+            }
+        }
+    )
+    def test_default_storage(self):
+        """ Test that "default" storage is used when no alias is provided """
+        self.assertIsInstance(lazy_initialize_storage_class(), FooTestingStorage)

import_export_celery/fields.py

@@ -1,27 +1,25 @@
-from django.conf import settings
 from django.db import models
 
 
 def lazy_initialize_storage_class():
-    # If the user has specified a custom storage backend, use it.
-    if settings.STORAGES.get("IMPORT_EXPORT_CELERY_STORAGE"):
-        try:
-            # From Django 4.2 and later
-            from django.core.files.storage import storages
-            from django.core.files.storage.handler import InvalidStorageError
-            try:
-                storage_class = storages['IMPORT_EXPORT_CELERY_STORAGE']
-            except InvalidStorageError:
-                from django.utils.module_loading import import_string
-                storage_class = settings.DEFAULT_FILE_STORAGE
-                storage_class = import_string(storage_class)()
-        except ImportError:
-            # Deprecated since Django 4.2, Removed in Django 5.1
-            from django.core.files.storage import get_storage_class
-            storage_class = get_storage_class(
-                settings.STORAGES.get("IMPORT_EXPORT_CELERY_STORAGE")["BACKEND"]
-            )()
-        return storage_class
+    from django.conf import settings
+    try:
+        from django.core.files.storage import storages
+        storages_defined = True
+    except ImportError:
+        storages_defined = False
+
+    if not hasattr(settings, 'IMPORT_EXPORT_CELERY_STORAGE') and storages_defined:
+        # Use new style storages if defined
+        storage_alias = getattr(settings, "IMPORT_EXPORT_CELERY_STORAGE_ALIAS", "default")
+        storage_class = storages[storage_alias]
+    else:
+        # Use old style storages if defined
+        from django.core.files.storage import get_storage_class
+        storage_class = get_storage_class(getattr(settings, "IMPORT_EXPORT_CELERY_STORAGE", "django.core.files.storage.FileSystemStorage"))
+        return storage_class()
+
+    return storage_class
 
 
 class ImportExportFileField(models.FileField):