Fix model validation exclusions. Fixes #500. Fixes #506.

4 files changed, 16 insertions, 13 deletions

diff --git a/docs/topics/release-notes.md b/docs/topics/release-notes.md
index 4ea393af..6d7dc348 100644
--- a/docs/topics/release-notes.md
+++ b/docs/topics/release-notes.md
@@ -8,6 +8,7 @@
 
 ### Master
 
+* Bugfix: Ensure read-only fields don't have model validation applied.
 * Bugfix: Fix hyperlinked fields in paginated results.
 
 ### 2.1.9
diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index da588082..d3ef8f77 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -32,6 +32,7 @@ def is_simple_callable(obj):
 
 
 class Field(object):
+    read_only = True
     creation_counter = 0
     empty = ''
     type_name = None
diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index 8026205e..1d93f777 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -128,17 +128,6 @@ class BaseSerializer(Field):
         """
         return {}
 
-    def get_excluded_fieldnames(self):
-        """
-        Returns the fieldnames that should not be validated.
-        """
-        excluded_fields = list(self.opts.exclude)
-        if self.opts.fields:
-            for field in self.fields.keys() + self.get_default_fields().keys():
-                if field not in list(self.opts.fields) + excluded_fields:
-                    excluded_fields.append(field)
-        return excluded_fields
-
     def get_fields(self):
         """
         Returns the complete set of fields for the object as a dict.
@@ -491,6 +480,18 @@ class ModelSerializer(Serializer):
         except KeyError:
             return ModelField(model_field=model_field, **kwargs)
 
+    def get_validation_exclusions(self):
+        """
+        Return a list of field names to exclude from model validation.
+        """
+        cls = self.opts.model
+        opts = get_concrete_model(cls)._meta
+        exclusions = [field.name for field in opts.fields + opts.many_to_many]
+        for field_name, field in self.fields.items():
+            if field_name in exclusions and not field.read_only:
+                exclusions.remove(field_name)
+        return exclusions
+
     def restore_object(self, attrs, instance=None):
         """
         Restore the model instance.
@@ -515,7 +516,7 @@ class ModelSerializer(Serializer):
 
         instance = self.opts.model(**attrs)
         try:
-            instance.full_clean(exclude=list(self.get_excluded_fieldnames()))
+            instance.full_clean(exclude=self.get_validation_exclusions())
         except ValidationError, err:
             self._errors = err.message_dict
             return None
diff --git a/rest_framework/tests/models.py b/rest_framework/tests/models.py
index 428bf130..e2b287d0 100644
--- a/rest_framework/tests/models.py
+++ b/rest_framework/tests/models.py
@@ -61,7 +61,7 @@ class BasicModel(RESTFrameworkModel):
 
 class SlugBasedModel(RESTFrameworkModel):
     text = models.CharField(max_length=100)
-    slug = models.SlugField(max_length=32, blank=True)
+    slug = models.SlugField(max_length=32)
 
 
 class DefaultValueModel(RESTFrameworkModel):