Remove use of storage wrappers

Use a dynamic subclass instead that always deconstructs to a fake
subclass with a __eq__ method that always returns True. This should
trick makemigrations into never creating a new migrations for
changes to the storage class or the arguments.

Signed-off-by: Roberto Rosario <Roberto.Rosario@mayan-edms.com>

mayan/apps/common/classes.py

@@ -72,6 +72,16 @@ class ErrorLogNamespace(object):
         return ErrorLogEntry.objects.filter(namespace=self.name)
 
 
+class FakeStorageSubclass(object):
+    """
+    Placeholder class to allow serializing the real storage subclass to
+    support migrations.
+    """
+
+    def __eq__(self, other):
+        return True
+
+
 class MissingItem(object):
     _registry = []
 

mayan/apps/common/migrations/0011_auto_20181229_0738.py

@@ -1,10 +1,10 @@
 # -*- coding: utf-8 -*-
-# Generated by Django 1.11.16 on 2018-12-28 04:22
+# Generated by Django 1.11.16 on 2018-12-29 07:38
 from __future__ import unicode_literals
 
 from django.db import migrations, models
+import mayan.apps.common.classes
 import mayan.apps.common.models
-import mayan.apps.common.storages
 
 
 class Migration(migrations.Migration):
@@ -17,6 +17,6 @@ class Migration(migrations.Migration):
         migrations.AlterField(
             model_name='shareduploadedfile',
             name='file',
-            field=models.FileField(storage=mayan.apps.common.storages.storage_sharedupload_wrapper, upload_to=mayan.apps.common.models.upload_to, verbose_name='File'),
+            field=models.FileField(storage=mayan.apps.common.classes.FakeStorageSubclass(), upload_to=mayan.apps.common.models.upload_to, verbose_name='File'),
         ),
     ]

mayan/apps/common/models.py

@@ -13,7 +13,7 @@ from django.utils.encoding import force_text, python_2_unicode_compatible
 from django.utils.translation import ugettext_lazy as _
 
 from .managers import ErrorLogEntryManager, UserLocaleProfileManager
-from .storages import storage_sharedupload_wrapper
+from .storages import storage_sharedupload
 
 logger = logging.getLogger(__name__)
 
@@ -58,7 +58,7 @@ class SharedUploadedFile(models.Model):
     that runs out of process.
     """
     file = models.FileField(
-        storage=storage_sharedupload_wrapper, upload_to=upload_to,
+        storage=storage_sharedupload, upload_to=upload_to,
         verbose_name=_('File')
     )
     filename = models.CharField(max_length=255, verbose_name=_('Filename'))

mayan/apps/common/storages.py

@@ -1,13 +1,8 @@
 from __future__ import unicode_literals
 
-from django.utils.module_loading import import_string
-
 from .settings import setting_shared_storage, setting_shared_storage_arguments
+from .utils import get_storage_subclass
 
-storage_sharedupload = import_string(
+storage_sharedupload = get_storage_subclass(
     dotted_path=setting_shared_storage.value
 )(**setting_shared_storage_arguments.value)
-
-
-def storage_sharedupload_wrapper():
-    return storage_sharedupload

mayan/apps/common/utils.py

@@ -12,6 +12,7 @@ from django.urls.base import get_script_prefix
 from django.utils.datastructures import MultiValueDict
 from django.utils.http import urlencode as django_urlencode
 from django.utils.http import urlquote as django_urlquote
+from django.utils.module_loading import import_string
 from django.utils.six.moves import reduce as reduce_function
 from django.utils.six.moves import xmlrpc_client
 
@@ -100,6 +101,28 @@ def get_descriptor(file_input, read=True):
         return file_input
 
 
+def get_storage_subclass(dotted_path):
+    """
+    Import a storage class and return a subclass that will always return eq
+    True to avoid creating a new migration when for runtime storage class
+    changes.
+    """
+    imported_storage_class = import_string(dotted_path=dotted_path)
+
+    class StorageSubclass(imported_storage_class):
+        def __init__(self, *args, **kwargs):
+            return super(StorageSubclass, self).__init__(*args, **kwargs)
+
+        def __eq__(self, other):
+            return True
+
+        def deconstruct(self):
+            return ('mayan.apps.common.classes.FakeStorageSubclass', (), {})
+
+
+    return StorageSubclass
+
+
 def TemporaryFile(*args, **kwargs):
     kwargs.update({'dir': setting_temporary_directory.value})
     return tempfile.TemporaryFile(*args, **kwargs)