Fixed #25160 -- Moved unsaved model instance data loss check to Model.save()

This mostly reverts 5643a3b51be338196d0b292d5626ad43648448d3 and
81e1a35c364e5353d2bf99368ad30a4184fbb653.

Thanks Carl Meyer for review.

2 files changed, 14 insertions, 22 deletions

diff --git a/docs/topics/db/examples/many_to_one.txt b/docs/topics/db/examples/many_to_one.txt
index 10020a83cb..efa5c37f3b 100644
--- a/docs/topics/db/examples/many_to_one.txt
+++ b/docs/topics/db/examples/many_to_one.txt
@@ -55,19 +55,17 @@ relationship. For example, creating an ``Article`` with unsaved ``Reporter``
 raises ``ValueError``::
 
     >>> r3 = Reporter(first_name='John', last_name='Smith', email='john@example.com')
-    >>> Article(headline="This is a test", pub_date=date(2005, 7, 27), reporter=r3)
+    >>> Article.objects.create(headline="This is a test", pub_date=date(2005, 7, 27), reporter=r3)
     Traceback (most recent call last):
     ...
-    ValueError: 'Cannot assign "<Reporter: John Smith>": "Reporter" instance isn't saved in the database.'
+    ValueError: save() prohibited to prevent data loss due to unsaved related object 'reporter'.
 
-If you want to disable the unsaved instance check, you can use the
-:attr:`~django.db.models.ForeignKey.allow_unsaved_instance_assignment`
-attribute.
+.. versionchanged:: 1.8.4
 
-.. versionchanged:: 1.8
-
-    Previously, assigning unsaved objects did not raise an error and could
-    result in silent data loss.
+    Previously, saving an object with unsaved related objects did not raise an
+    error and could result in silent data loss. In 1.8-1.8.3, unsaved model
+    instances couldn't be assigned to related fields, but this restriction was
+    removed to allow easier usage of in-memory models.
 
 Article objects have access to their related Reporter objects::
 
diff --git a/docs/topics/db/examples/one_to_one.txt b/docs/topics/db/examples/one_to_one.txt
index 311ff75d8d..97c5b5c4b1 100644
--- a/docs/topics/db/examples/one_to_one.txt
+++ b/docs/topics/db/examples/one_to_one.txt
@@ -96,23 +96,17 @@ relationship. For example, creating an ``Restaurant`` with unsaved ``Place``
 raises ``ValueError``::
 
     >>> p3 = Place(name='Demon Dogs', address='944 W. Fullerton')
-    >>> Restaurant(place=p3, serves_hot_dogs=True, serves_pizza=False)
+    >>> Restaurant.objects.create(place=p3, serves_hot_dogs=True, serves_pizza=False)
     Traceback (most recent call last):
     ...
-    ValueError: 'Cannot assign "<Place: Demon Dogs>": "Place" instance isn't saved in the database.'
-    >>> p.restaurant = Restaurant(place=p, serves_hot_dogs=True, serves_pizza=False)
-    Traceback (most recent call last):
-    ...
-    ValueError: 'Cannot assign "<Restaurant: Demon Dogs the restaurant>": "Restaurant" instance isn't saved in the database.'
-
-If you want to disable the unsaved instance check, you can use the
-:attr:`~django.db.models.ForeignKey.allow_unsaved_instance_assignment`
-attribute.
+    ValueError: save() prohibited to prevent data loss due to unsaved related object 'place'.
 
-.. versionchanged:: 1.8
+.. versionchanged:: 1.8.4
 
-    Previously, assigning unsaved objects did not raise an error and could
-    result in silent data loss.
+    Previously, saving an object with unsaved related objects did not raise an
+    error and could result in silent data loss. In 1.8-1.8.3, unsaved model
+    instances couldn't be assigned to related fields, but this restriction was
+    removed to allow easier usage of in-memory models.
 
 Restaurant.objects.all() just returns the Restaurants, not the Places.  Note
 that there are two restaurants - Ace Hardware the Restaurant was created in the