From ab173fd8f9070ccdb70f86f400d2ffa780977ce4 Mon Sep 17 00:00:00 2001
From: Tom Christie <tom@tomchristie.com>
Date: Tue, 2 Oct 2012 15:37:13 +0100
Subject: [PATCH] Fix bug where pk could be set in post data

---
 docs/api-guide/serializers.md    |  3 +++
 rest_framework/serializers.py    | 22 ++++++++++++++++++----
 rest_framework/tests/generics.py | 12 ++++++++++++
 3 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/docs/api-guide/serializers.md b/docs/api-guide/serializers.md
index 38a1e560e..4ddc6e0af 100644
--- a/docs/api-guide/serializers.md
+++ b/docs/api-guide/serializers.md
@@ -230,6 +230,9 @@ The `nested` option may also be set by passing it to the `serialize()` method.
         class Meta:
             model = Account
 
+        def get_pk_field(self, model_field):
+            return Field(readonly=True)
+
         def get_nested_field(self, model_field):
             return ModelSerializer()
 
diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index bb48e3817..d0d34094b 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -308,17 +308,31 @@ class ModelSerializer(RelatedField, Serializer):
         fields += [field for field in opts.many_to_many if field.serialize]
 
         ret = SortedDict()
+        is_pk = True  # First field in the list is the pk
+
         for model_field in fields:
-            if model_field.rel and nested:
+            if is_pk:
+                field = self.get_pk_field(model_field)
+                is_pk = False
+            elif model_field.rel and nested:
                 field = self.get_nested_field(model_field)
             elif model_field.rel:
                 field = self.get_related_field(model_field)
             else:
                 field = self.get_field(model_field)
-            field.initialize(parent=self, model_field=model_field)
-            ret[model_field.name] = field
+
+            if field is not None:
+                field.initialize(parent=self, model_field=model_field)
+                ret[model_field.name] = field
+
         return ret
 
+    def get_pk_field(self, model_field):
+        """
+        Returns a default instance of the pk field.
+        """
+        return Field(readonly=True)
+
     def get_nested_field(self, model_field):
         """
         Creates a default instance of a nested relational field.
@@ -333,7 +347,7 @@ class ModelSerializer(RelatedField, Serializer):
 
     def get_field(self, model_field):
         """
-        Creates a default instance of a basic field.
+        Creates a default instance of a basic non-relational field.
         """
         return Field()
 
diff --git a/rest_framework/tests/generics.py b/rest_framework/tests/generics.py
index ec46b427f..79c01f9e2 100644
--- a/rest_framework/tests/generics.py
+++ b/rest_framework/tests/generics.py
@@ -100,6 +100,18 @@ class TestRootView(TestCase):
         self.assertEquals(response.status_code, status.HTTP_200_OK)
         self.assertEquals(response.data, expected)
 
+    def test_post_cannot_set_id(self):
+        """
+        POST requests to create a new object should not be able to set the id.
+        """
+        content = {'id': 999, 'text': 'foobar'}
+        request = factory.post('/', json.dumps(content), content_type='application/json')
+        response = self.view(request).render()
+        self.assertEquals(response.status_code, status.HTTP_201_CREATED)
+        self.assertEquals(response.data, {'id': 4, 'text': u'foobar'})
+        created = self.objects.get(id=4)
+        self.assertEquals(created.text, 'foobar')
+
 
 class TestInstanceView(TestCase):
     def setUp(self):