From 3500b210386b70741e8b6724dea5d916ad5f0c8f Mon Sep 17 00:00:00 2001
From: Krzysztof Nazarewski <nazarewk@gmail.com>
Date: Wed, 9 Mar 2016 16:00:47 +0100
Subject: [PATCH 1/3] fixed PrimaryKeyRelatedField(required=False, ...) with
 missing data

---
 rest_framework/fields.py    | 8 +++++++-
 rest_framework/relations.py | 2 +-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 2a08e09ff..587ecc697 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -62,7 +62,7 @@ def is_simple_callable(obj):
     return len_args <= len_defaults
 
 
-def get_attribute(instance, attrs):
+def get_attribute(instance, attrs, required=True):
     """
     Similar to Python's built in `getattr(instance, attr)`,
     but takes a list of nested attributes, instead of a single attribute.
@@ -80,6 +80,12 @@ def get_attribute(instance, attrs):
                 instance = getattr(instance, attr)
         except ObjectDoesNotExist:
             return None
+        # RelatedObjectDoesNotExist inherits from both ObjectDoesNotExist and
+        # AttributeError, so ObjectDoesNotExist has to come first
+        except (AttributeError, KeyError):
+            if not required:
+                raise SkipField
+            raise
         if is_simple_callable(instance):
             try:
                 instance = instance()
diff --git a/rest_framework/relations.py b/rest_framework/relations.py
index 572b69170..f695e79ba 100644
--- a/rest_framework/relations.py
+++ b/rest_framework/relations.py
@@ -154,7 +154,7 @@ class RelatedField(Field):
                 pass
 
         # Standard case, return the object instance.
-        return get_attribute(instance, self.source_attrs)
+        return get_attribute(instance, self.source_attrs, self.required)
 
     @property
     def choices(self):

From bee7b7a18206555d8b570d254401f52700d0275a Mon Sep 17 00:00:00 2001
From: Krzysztof Nazarewski <nazarewk@gmail.com>
Date: Fri, 11 Mar 2016 12:54:31 +0100
Subject: [PATCH 2/3] added ModelSerializer test failing with the same error

---
 tests/test_relations_pk.py | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/tests/test_relations_pk.py b/tests/test_relations_pk.py
index 169f7d9c5..470c51410 100644
--- a/tests/test_relations_pk.py
+++ b/tests/test_relations_pk.py
@@ -327,6 +327,23 @@ class PKForeignKeyTests(TestCase):
         serializer = NullableForeignKeySourceSerializer()
         self.assertEqual(serializer.data['target'], None)
 
+    def test_foreign_key_not_required(self):
+        """
+        Let's say we wanted to fill the non-nullable model field inside
+        Model.save(), we would make it empty and not required.
+        """
+        class ModelSerializer(ForeignKeySourceSerializer):
+            class Meta(ForeignKeySourceSerializer.Meta):
+                extra_kwargs = {
+                    'target': {
+                        'required': False,
+                        'allow_empty': True,
+                    }
+                }
+        serializer = ModelSerializer(data={'name': 'test'})
+        serializer.is_valid(raise_exception=True)
+        self.assertNotIn('target', serializer.data)
+
 
 class PKNullableForeignKeyTests(TestCase):
     def setUp(self):

From 45235e19cb5b9a200648da118324fbf8bb38c5d5 Mon Sep 17 00:00:00 2001
From: Krzysztof Nazarewski <nazarewk@gmail.com>
Date: Fri, 11 Mar 2016 14:09:00 +0100
Subject: [PATCH 3/3] removed everything but required from extra_kwargs

---
 tests/test_relations_pk.py | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/tests/test_relations_pk.py b/tests/test_relations_pk.py
index 470c51410..e9060d707 100644
--- a/tests/test_relations_pk.py
+++ b/tests/test_relations_pk.py
@@ -334,12 +334,7 @@ class PKForeignKeyTests(TestCase):
         """
         class ModelSerializer(ForeignKeySourceSerializer):
             class Meta(ForeignKeySourceSerializer.Meta):
-                extra_kwargs = {
-                    'target': {
-                        'required': False,
-                        'allow_empty': True,
-                    }
-                }
+                extra_kwargs = {'target': {'required': False}}
         serializer = ModelSerializer(data={'name': 'test'})
         serializer.is_valid(raise_exception=True)
         self.assertNotIn('target', serializer.data)