Fixed #6445 -- Allow model instances to be used as a default for ForeignKeys

(via a callable). Also updates the documentation of the "default" attribute to
indicate a callable can be used. Thanks, Philipe Raoult.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7331 bcc190cf-cafb-0310-a4f2-bffc1f526a37

3 files changed, 33 insertions, 1 deletions

diff --git a/django/db/models/fields/related.py b/django/db/models/fields/related.py
index ba1cfd5435..c87fdd90c1 100644
--- a/django/db/models/fields/related.py
+++ b/django/db/models/fields/related.py
@@ -548,6 +548,13 @@ class ForeignKey(RelatedField, Field):
             params['choices'] = self.get_choices_default()
         return field_objs, params
 
+    def get_default(self):
+        "Here we check if the default value is an object and return the to_field if so."
+        field_default = super(ForeignKey, self).get_default()
+        if isinstance(field_default, self.rel.to):
+            return getattr(field_default, self.rel.get_related_field().attname)
+        return field_default
+
     def get_manipulator_field_objs(self):
         rel_field = self.rel.get_related_field()
         if self.rel.raw_id_admin and not isinstance(rel_field, AutoField):
diff --git a/docs/model-api.txt b/docs/model-api.txt
index 16a45f629e..f73c5aadf7 100644
--- a/docs/model-api.txt
+++ b/docs/model-api.txt
@@ -626,7 +626,8 @@ option is ignored.
 ``default``
 ~~~~~~~~~~~
 
-The default value for the field.
+The default value for the field. This can be a value or a callable object. If
+callable it will be called every time a new object is created.
 
 ``editable``
 ~~~~~~~~~~~~
diff --git a/tests/regressiontests/model_fields/models.py b/tests/regressiontests/model_fields/models.py
index e69de29bb2..7e07227961 100644
--- a/tests/regressiontests/model_fields/models.py
+++ b/tests/regressiontests/model_fields/models.py
@@ -0,0 +1,24 @@
+
+from django.db import models
+
+class Foo(models.Model):
+    a = models.CharField(max_length=10)
+
+def get_foo():
+    return Foo.objects.get(id=1)
+
+class Bar(models.Model):
+    b = models.CharField(max_length=10)
+    a = models.ForeignKey(Foo, default=get_foo)
+
+__test__ = {'API_TESTS':"""
+# Create a couple of Places.
+>>> f = Foo.objects.create(a='abc')
+>>> f.id
+1
+>>> b = Bar(b = "bcd")
+>>> b.a
+<Foo: Foo object>
+>>> b.save()
+
+"""}