Fixed #26398 -- Made FieldFile.open() respect its mode argument.

django/db/models/fields/files.py

@@ -42,10 +42,10 @@ class FieldFile(File):
         if not self:
             raise ValueError("The '%s' attribute has no file associated with it." % self.field.name)
 
-    def _get_file(self):
+    def _get_file(self, mode='rb'):
         self._require_file()
         if not hasattr(self, '_file') or self._file is None:
-            self._file = self.storage.open(self.name, 'rb')
+            self._file = self.storage.open(self.name, mode)
         return self._file
 
     def _set_file(self, file):
@@ -74,8 +74,7 @@ class FieldFile(File):
     size = property(_get_size)
 
     def open(self, mode='rb'):
-        self._require_file()
-        self.file.open(mode)
+        self._get_file(mode)
     # open() doesn't alter the file's contents, but it does reset the pointer
     open.alters_data = True
 

tests/file_storage/tests.py

@@ -710,6 +710,16 @@ class FileFieldStorageTests(TestCase):
         self.assertEqual(list(obj.normal.chunks(chunk_size=2)), [b"co", b"nt", b"en", b"t"])
         obj.normal.close()
 
+    def test_filefield_write(self):
+        # Files can be written to.
+        obj = Storage.objects.create(normal=SimpleUploadedFile('rewritten.txt', b'content'))
+        with obj.normal as normal:
+            normal.open('wb')
+            normal.write(b'updated')
+        obj.refresh_from_db()
+        self.assertEqual(obj.normal.read(), b'updated')
+        obj.normal.close()
+
     def test_duplicate_filename(self):
         # Multiple files with the same name get _(7 random chars) appended to them.
         objs = [Storage() for i in range(2)]