Don't make a second migration if there was a force-null-default addcol.

django/db/migrations/autodetector.py

@@ -188,15 +188,26 @@ class MigrationAutodetector(object):
                     continue
                 # You can't just add NOT NULL fields with no default
                 if not field.null and not field.has_default():
+                    field = field.clone()
                     field.default = self.questioner.ask_not_null_addition(field_name, model_name)
-                self.add_to_migration(
-                    app_label,
-                    operations.AddField(
-                        model_name=model_name,
-                        name=field_name,
-                        field=field,
+                    self.add_to_migration(
+                        app_label,
+                        operations.AddField(
+                            model_name=model_name,
+                            name=field_name,
+                            field=field,
+                            preserve_default=False,
+                        )
+                    )
+                else:
+                    self.add_to_migration(
+                        app_label,
+                        operations.AddField(
+                            model_name=model_name,
+                            name=field_name,
+                            field=field,
+                        )
                     )
-                )
             # Old fields
             for field_name in old_field_names - new_field_names:
                 self.add_to_migration(
@@ -434,7 +445,8 @@ class InteractiveMigrationQuestioner(MigrationQuestioner):
         "Adding a NOT NULL field to a model"
         choice = self._choice_input(
             "You are trying to add a non-nullable field '%s' to %s without a default;\n" % (field_name, model_name) +
-            "this is not possible. Please select a fix:",
+            "we can't do that (the database needs something to populate existing rows).\n" +
+            "Please select a fix:",
             [
                 "Provide a one-off default now (will be set on all existing rows)",
                 "Quit, and let me add a default in models.py",

django/db/migrations/operations/fields.py

@@ -1,4 +1,5 @@
 from django.db import router
+from django.db.models.fields import NOT_PROVIDED
 from .base import Operation
 
 
@@ -7,13 +8,20 @@ class AddField(Operation):
     Adds a field to a model.
     """
 
-    def __init__(self, model_name, name, field):
+    def __init__(self, model_name, name, field, preserve_default=True):
         self.model_name = model_name
         self.name = name
         self.field = field
+        self.preserve_default = preserve_default
 
     def state_forwards(self, app_label, state):
-        state.models[app_label, self.model_name.lower()].fields.append((self.name, self.field))
+        # If preserve default is off, don't use the default for future state
+        if not self.preserve_default:
+            field = self.field.clone()
+            field.default = NOT_PROVIDED
+        else:
+            field = self.field
+        state.models[app_label, self.model_name.lower()].fields.append((self.name, field))
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
         from_model = from_state.render().get_model(app_label, self.model_name)