Fixed #25005 -- Made date and time fields with auto_now/auto_now_add use effective default.

Thanks to Andriy Sokolovskiy for initial patch.

django/db/backends/base/schema.py

@@ -1,9 +1,10 @@
 import hashlib
 import logging
+from datetime import datetime
 
 from django.db.backends.utils import truncate_name
 from django.db.transaction import atomic
-from django.utils import six
+from django.utils import six, timezone
 from django.utils.encoding import force_bytes
 
 logger = logging.getLogger('django.db.backends.schema')
@@ -201,6 +202,15 @@ class BaseDatabaseSchemaEditor(object):
                 default = six.binary_type()
             else:
                 default = six.text_type()
+        elif getattr(field, 'auto_now', False) or getattr(field, 'auto_now_add', False):
+            default = datetime.now()
+            internal_type = field.get_internal_type()
+            if internal_type == 'DateField':
+                default = default.date
+            elif internal_type == 'TimeField':
+                default = default.time
+            elif internal_type == 'DateTimeField':
+                default = timezone.now
         else:
             default = None
         # If it's a callable, call it

django/db/migrations/autodetector.py

@@ -802,10 +802,16 @@ class MigrationAutodetector(object):
         # You can't just add NOT NULL fields with no default or fields
         # which don't allow empty strings as default.
         preserve_default = True
-        if (not field.null and not field.has_default() and not field.many_to_many and
-                not (field.blank and field.empty_strings_allowed)):
+        time_fields = (models.DateField, models.DateTimeField, models.TimeField)
+        if (not field.null and not field.has_default() and
+                not field.many_to_many and
+                not (field.blank and field.empty_strings_allowed) and
+                not (isinstance(field, time_fields) and field.auto_now)):
             field = field.clone()
-            field.default = self.questioner.ask_not_null_addition(field_name, model_name)
+            if isinstance(field, time_fields) and field.auto_now_add:
+                field.default = self.questioner.ask_auto_now_add_addition(field_name, model_name)
+            else:
+                field.default = self.questioner.ask_not_null_addition(field_name, model_name)
             preserve_default = False
         self.add_operation(
             app_label,

django/db/migrations/questioner.py

@@ -76,6 +76,11 @@ class MigrationQuestioner(object):
         "Do you really want to merge these migrations?"
         return self.defaults.get("ask_merge", False)
 
+    def ask_auto_now_add_addition(self, field_name, model_name):
+        "Adding an auto_now_add field to a model"
+        # None means quit
+        return None
+
 
 class InteractiveMigrationQuestioner(MigrationQuestioner):
 
@@ -101,17 +106,36 @@ class InteractiveMigrationQuestioner(MigrationQuestioner):
                 pass
             result = input("Please select a valid option: ")
 
-    def _ask_default(self):
+    def _ask_default(self, default=''):
+        """
+        Prompt for a default value.
+
+        The ``default`` argument allows providing a custom default value (as a
+        string) which will be shown to the user and used as the return value
+        if the user doesn't provide any other input.
+        """
         print("Please enter the default value now, as valid Python")
+        if default:
+            print(
+                "You can accept the default '{}' by pressing 'Enter' or you "
+                "can provide another value.".format(default)
+            )
         print("The datetime and django.utils.timezone modules are available, so you can do e.g. timezone.now")
+        print("Type 'exit' to exit this prompt")
         while True:
+            if default:
+                prompt = "[default: {}] >>> ".format(default)
+            else:
+                prompt = ">>> "
             if six.PY3:
                 # Six does not correctly abstract over the fact that
                 # py3 input returns a unicode string, while py2 raw_input
                 # returns a bytestring.
-                code = input(">>> ")
+                code = input(prompt)
             else:
-                code = input(">>> ").decode(sys.stdin.encoding)
+                code = input(prompt).decode(sys.stdin.encoding)
+            if not code and default:
+                code = default
             if not code:
                 print("Please enter some code, or 'exit' (with no quotes) to exit.")
             elif code == "exit":
@@ -186,6 +210,25 @@ class InteractiveMigrationQuestioner(MigrationQuestioner):
             False,
         )
 
+    def ask_auto_now_add_addition(self, field_name, model_name):
+        "Adding an auto_now_add field to a model"
+        if not self.dry_run:
+            choice = self._choice_input(
+                "You are trying to add the field '{}' with 'auto_now_add=True' "
+                "to {} without a default; the database needs something to "
+                "populate existing rows.\n".format(field_name, model_name),
+                [
+                    "Provide a one-off default now (will be set on all "
+                    "existing rows)",
+                    "Quit, and let me add a default in models.py",
+                ]
+            )
+            if choice == 2:
+                sys.exit(3)
+            else:
+                return self._ask_default(default='timezone.now')
+        return None
+
 
 class NonInteractiveMigrationQuestioner(MigrationQuestioner):
 
@@ -196,3 +239,7 @@ class NonInteractiveMigrationQuestioner(MigrationQuestioner):
     def ask_not_null_alteration(self, field_name, model_name):
         # We can't ask the user, so set as not provided.
         return NOT_PROVIDED
+
+    def ask_auto_now_add_addition(self, field_name, model_name):
+        # We can't ask the user, so act like the user aborted.
+        sys.exit(3)