Fixed #28184 -- Allowed using a callable for FileField and ImageField storage.

3 files changed, 40 insertions, 2 deletions

diff --git a/docs/ref/models/fields.txt b/docs/ref/models/fields.txt
index 7c5401046b..7ca0b96d85 100644
--- a/docs/ref/models/fields.txt
+++ b/docs/ref/models/fields.txt
@@ -822,8 +822,13 @@ Has two optional arguments:
 
 .. attribute:: FileField.storage
 
-    A storage object, which handles the storage and retrieval of your
-    files. See :doc:`/topics/files` for details on how to provide this object.
+    A storage object, or a callable which returns a storage object. This
+    handles the storage and retrieval of your files. See :doc:`/topics/files`
+    for details on how to provide this object.
+
+    .. versionchanged:: 3.1
+
+        The ability to provide a callable was added.
 
 The default form widget for this field is a
 :class:`~django.forms.ClearableFileInput`.
diff --git a/docs/releases/3.1.txt b/docs/releases/3.1.txt
index fd1bd4f40c..7df81329b4 100644
--- a/docs/releases/3.1.txt
+++ b/docs/releases/3.1.txt
@@ -248,6 +248,11 @@ File Storage
 
 * ``FileSystemStorage.save()`` method now supports :class:`pathlib.Path`.
 
+* :class:`~django.db.models.FileField` and
+  :class:`~django.db.models.ImageField` now accept a callable for ``storage``.
+  This allows you to modify the used storage at runtime, selecting different
+  storages for different environments, for example.
+
 File Uploads
 ~~~~~~~~~~~~
 
diff --git a/docs/topics/files.txt b/docs/topics/files.txt
index dbe9549818..73d0a11fff 100644
--- a/docs/topics/files.txt
+++ b/docs/topics/files.txt
@@ -202,3 +202,31 @@ For example, the following code will store uploaded files under
 :doc:`Custom storage systems </howto/custom-file-storage>` work the same way:
 you can pass them in as the ``storage`` argument to a
 :class:`~django.db.models.FileField`.
+
+Using a callable
+----------------
+
+.. versionadded:: 3.1
+
+You can use a callable as the :attr:`~django.db.models.FileField.storage`
+parameter for :class:`~django.db.models.FileField` or
+:class:`~django.db.models.ImageField`. This allows you to modify the used
+storage at runtime, selecting different storages for different environments,
+for example.
+
+Your callable will be evaluated when your models classes are loaded, and must
+return an instance of :class:`~django.core.files.storage.Storage`.
+
+For example::
+
+    from django.conf import settings
+    from django.db import models
+    from .storages import MyLocalStorage, MyRemoteStorage
+
+
+    def select_storage():
+        return MyLocalStorage() if settings.DEBUG else MyRemoteStorage()
+
+
+    class MyModel(models.Model):
+        my_file = models.FileField(storage=select_storage)