Fix manager migration (fixes #1)

docs/upgrading.rst

@@ -17,6 +17,15 @@ There are no upgrade instructions yet.
 Changelog
 =========
 
+1.0.1, 2018-10-
+-----------------
+
+Bugfix:
+
+* Managers on registered models which set ``use_in_migrations`` can now be
+  serialised for migrations.
+
+
 1.0.0, 2018-09-16
 -----------------
 

gdpr_assist/models.py

@@ -56,9 +56,11 @@ def _cast_class(cls, queryset):
 class PrivacyManager(models.Manager):
     """
     A manager with support for anonymising data
+
+    Don't subclass this directly - write your manager as normal, this will be
+    applied automatically.
     """
-    # The class of a privacy queryset. Here so a custom PrivacyManager can
-    # replace it with a custom PrivacyQuerySet subclass.
+    # The class of a privacy queryset.
     privacy_queryset = PrivacyQuerySet
 
     def _enhance_queryset(self, qs):
@@ -91,6 +93,22 @@ def _cast_class(cls, manager):
         )
         return manager
 
+    def deconstruct(self):
+        """
+        Deconstruct the original manager - it will be cast again next time.
+        """
+        # Check bases are as expected from _cast_class
+        bases = self.__class__.__bases__
+        if len(bases) != 2:
+            raise ValueError('Unexpected base classes for CastPrivacyManager')
+
+        # Original is second - instatiate and deconstruct it
+        orig_cls = bases[1]
+        orig_args = self._constructor_args[0]
+        orig_kwargs = self._constructor_args[1]
+        orig_manager = orig_cls(*orig_args, **orig_kwargs)
+        return orig_manager.deconstruct()
+
 
 class PrivacyMeta(object):
     fields = None

tests/base.py

@@ -0,0 +1,35 @@
+"""
+Base classes for tests
+"""
+from django.db.migrations.writer import MigrationWriter
+from django.test import TestCase
+
+
+class MigrationTestCase(TestCase):
+    """
+    Based on django.tests.migrations.test_+writer.WriterTests
+    """
+    def safe_exec(self, string, value=None):
+        d = {}
+        try:
+            exec(string, globals(), d)
+        except Exception as e:
+            if value:
+                self.fail("Could not exec %r (from value %r): %s" % (string.strip(), value, e))
+            else:
+                self.fail("Could not exec %r: %s" % (string.strip(), e))
+        return d
+
+    def serialize(self, value):
+        """
+        Test a value can be serialised by the MigrationWriter
+        """
+        string, imports = MigrationWriter.serialize(value)
+        return string, imports
+
+    def serialize_round_trip(self, value):
+        """
+        Test a value can be serialised and deserialised
+        """
+        string, imports = self.serialize(value)
+        return self.safe_exec("%s\ntest_value_result = %s" % ("\n".join(imports), string), value)['test_value_result']

tests/test_anonymisation.py

@@ -9,7 +9,6 @@
 import uuid
 
 from django.db import models
-from django.db.migrations.writer import MigrationWriter
 from django.test import TestCase
 
 from model_mommy import mommy
@@ -28,6 +27,7 @@
     ForeignKeyModel,
     ForeignKeyToUnregisteredModel,
 )
+from .base import MigrationTestCase
 
 
 class TestAnonymisationBase(TestCase):
@@ -63,27 +63,12 @@ def test_anonymise_action__protect__raises_error(self):
         self.assertEqual('Cannot ANONYMISE(PROTECT)', str(cm.exception))
 
 
-class TestOnDeleteAnonymiseDeconstruct(TestCase):
+class TestOnDeleteAnonymiseDeconstruct(MigrationTestCase):
     """
-    Based on django.tests.migrations.test_+writer.WriterTests
+    Test on_delete=ANONYMISE can be deconstructed
     """
-    def safe_exec(self, string, value=None):
-        d = {}
-        try:
-            exec(string, globals(), d)
-        except Exception as e:
-            if value:
-                self.fail("Could not exec %r (from value %r): %s" % (string.strip(), value, e))
-            else:
-                self.fail("Could not exec %r: %s" % (string.strip(), e))
-        return d
-
-    def serialize_round_trip(self, value):
-        string, imports = MigrationWriter.serialize(value)
-        return self.safe_exec("%s\ntest_value_result = %s" % ("\n".join(imports), string), value)['test_value_result']
-
     def test_anonymise_deconstruct__deconstructs(self):
-        string, imports = MigrationWriter.serialize(
+        string, imports = self.serialize(
             gdpr_assist.ANONYMISE(models.SET_NULL),
         )
         self.assertEqual(

tests/test_model_meta.py

@@ -24,6 +24,7 @@
     ModelWithPrivacyMeta,
     ModelWithoutPrivacyMeta,
 )
+from .base import MigrationTestCase
 
 
 class TestRegistry(TestCase):
@@ -210,3 +211,17 @@ def test_validate_on_delete_anonymise__not_registered__raises_exception(self):
                 ),
                 str(cm.exception),
             )
+
+
+class TestRegisteredModelMigration(MigrationTestCase):
+    """
+    Check registered models can be migratated
+    """
+    def test_manager_deconstruct__deconstructs(self):
+        # This should serialise to the original manager
+        string, imports = self.serialize(ModelWithPrivacyMeta.objects)
+        self.assertEqual(string, 'django.db.models.manager.Manager()')
+
+        # And check it serialises back
+        obj = self.serialize_round_trip(ModelWithPrivacyMeta.objects)
+        self.assertIsInstance(obj, models.Manager)