Fixed #24495 -- Allowed unsaved model instance assignment check to be bypassed.

5 files changed, 52 insertions, 1 deletions

diff --git a/docs/ref/contrib/contenttypes.txt b/docs/ref/contrib/contenttypes.txt
index f741e30a37..ef50f84ce8 100644
--- a/docs/ref/contrib/contenttypes.txt
+++ b/docs/ref/contrib/contenttypes.txt
@@ -299,6 +299,13 @@ model:
        is ``True``. This mirrors the ``for_concrete_model`` argument to
        :meth:`~django.contrib.contenttypes.models.ContentTypeManager.get_for_model`.
 
+    .. attribute:: GenericForeignKey.allow_unsaved_instance_assignment
+
+        .. versionadded:: 1.8
+
+        Works analogously to :attr:`ForeignKey.allow_unsaved_instance_assignment
+        <django.db.models.ForeignKey.allow_unsaved_instance_assignment>`.
+
 .. admonition:: Primary key type compatibility
 
    The "object_id" field doesn't have to be the same type as the
diff --git a/docs/ref/models/fields.txt b/docs/ref/models/fields.txt
index d1fc04d3b5..9fd9bd7fa3 100644
--- a/docs/ref/models/fields.txt
+++ b/docs/ref/models/fields.txt
@@ -1291,6 +1291,30 @@ The possible values for :attr:`~ForeignKey.on_delete` are found in
 
     If in doubt, leave it to its default of ``True``.
 
+.. attribute:: ForeignKey.allow_unsaved_instance_assignment
+
+    .. versionadded:: 1.8
+
+        This flag was added for backwards compatibility as older versions of
+        Django always allowed assigning unsaved model instances.
+
+    Django prevents unsaved model instances from being assigned to a
+    ``ForeignKey`` field to prevent accidental data loss (unsaved foreign keys
+    are silently ignored when saving a model instance).
+
+    If you require allowing the assignment of unsaved instances and aren't
+    concerned about the data loss possibility (e.g. you never save the objects
+    to the database), you can disable this check by creating a subclass of the
+    field class and setting its ``allow_unsaved_instance_assignment`` attribute
+    to ``True``. For example::
+
+        class UnsavedForeignKey(models.ForeignKey):
+            # A ForeignKey which can point to an unsaved object
+            allow_unsaved_instance_assignment = True
+
+        class Book(models.Model):
+            author = UnsavedForeignKey(Author)
+
 .. _ref-manytomany:
 
 ``ManyToManyField``
@@ -1388,7 +1412,7 @@ that control how the relationship functions.
     * ``<other_model>_id``: the ``id`` of the model that the
       ``ManyToManyField`` points to.
 
-    If the ``ManyToManyField`` points from and to the same model, the following 
+    If the ``ManyToManyField`` points from and to the same model, the following
     fields are generated:
 
     * ``id``: the primary key of the relation.
@@ -1483,6 +1507,12 @@ that control how the relationship functions.
 
     If in doubt, leave it to its default of ``True``.
 
+.. attribute:: ManyToManyField.allow_unsaved_instance_assignment
+
+    .. versionadded:: 1.8
+
+    Works analogously to :attr:`ForeignKey.allow_unsaved_instance_assignment`.
+
 :class:`ManyToManyField` does not support :attr:`~Field.validators`.
 
 :attr:`~Field.null` has no effect since there is no way to require a
diff --git a/docs/releases/1.8.txt b/docs/releases/1.8.txt
index bbbe97a881..a0a27ee89e 100644
--- a/docs/releases/1.8.txt
+++ b/docs/releases/1.8.txt
@@ -713,6 +713,12 @@ Now, an error will be raised to prevent data loss::
     ...
     ValueError: Cannot assign "<Author: John>": "Author" instance isn't saved in the database.
 
+If you require allowing the assignment of unsaved instances (the old behavior)
+and aren't concerned about the data loss possibility (e.g. you never save the
+objects to the database), you can disable this check by using the
+:attr:`~django.db.models.ForeignKey.allow_unsaved_instance_assignment`
+attribute.
+
 Management commands that only accept positional arguments
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/docs/topics/db/examples/many_to_one.txt b/docs/topics/db/examples/many_to_one.txt
index c5c3e10034..e43809fd1c 100644
--- a/docs/topics/db/examples/many_to_one.txt
+++ b/docs/topics/db/examples/many_to_one.txt
@@ -60,6 +60,10 @@ raises ``ValueError``::
     ...
     ValueError: 'Cannot assign "<Reporter: John Smith>": "Reporter" 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.
+
 .. versionchanged:: 1.8
 
     Previously, assigning unsaved objects did not raise an error and could
diff --git a/docs/topics/db/examples/one_to_one.txt b/docs/topics/db/examples/one_to_one.txt
index f1bdf3de9c..f2a3f54508 100644
--- a/docs/topics/db/examples/one_to_one.txt
+++ b/docs/topics/db/examples/one_to_one.txt
@@ -101,6 +101,10 @@ raises ``ValueError``::
     ...
     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.
+
 .. versionchanged:: 1.8
 
     Previously, assigning unsaved objects did not raise an error and could