Allow to skip preference creation when checkpreferences is invoked (#257)

In some case you might not want to prefill the cache, only to cleanup
the removed preferences. Thus it would be convenient to skip the
creation steps.

Author: er-vin

dynamic_preferences/management/commands/checkpreferences.py

@@ -29,15 +29,25 @@ class Command(BaseCommand):
     help = (
         "Find and delete preferences from database if they don't exist in "
         "registries. Create preferences that are not present in database"
+        "(except when invoked with --skip_create)."
     )
 
+    def add_arguments(self, parser):
+        parser.add_argument(
+            "--skip_create",
+            action="store_true",
+            help="Forces to skip the creation step for missing preferences",
+        )
+
     def handle(self, *args, **options):
+        skip_create = options["skip_create"]
 
         # Create needed preferences
         # Global
-        self.stdout.write("Creating missing global preferences...")
-        manager = global_preferences_registry.manager()
-        manager.all()
+        if not skip_create:
+            self.stdout.write("Creating missing global preferences...")
+            manager = global_preferences_registry.manager()
+            manager.all()
 
         deleted = delete_preferences(GlobalPreferenceModel.objects.all())
         message = "Deleted {deleted} global preferences".format(
@@ -57,6 +67,9 @@ def handle(self, *args, **options):
             if not hasattr(preference_model, 'get_instance_model'):
                 continue
 
+            if skip_create:
+                continue
+
             message = (
                 "Creating missing preferences for {model} model...".format(
                     model=preference_model.get_instance_model().__name__,

tests/test_checkpreferences_command.py

@@ -33,3 +33,12 @@ def test_dry_run(self):
             "Creating missing preferences for User model...",
         ])
         self.assertEqual(out, expected_output)
+
+    def test_skip_create(self):
+        out = self.call_command("--skip_create", verbosity=0)
+        expected_output = "\n".join([
+            "Deleted 0 global preferences",
+            "Deleted 0 GlobalPreferenceModel preferences",
+            "Deleted 0 UserPreferenceModel preferences",
+        ])
+        self.assertEqual(out, expected_output)