From 770ed3de2ef8339ec0b74f7eb522283718e01a3b Mon Sep 17 00:00:00 2001
From: Ryan Kaskel
Date: Sat, 18 May 2013 13:11:40 +0100
Subject: ToMany fields default to read-only if targeting ManyToManyField.

---
 rest_framework/serializers.py | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

(limited to 'rest_framework/serializers.py')

diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index 7707de7a..75f1e1d0 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -587,11 +587,16 @@ class ModelSerializer(Serializer):
         forward_rels += [field for field in opts.many_to_many if field.serialize]
 
         for model_field in forward_rels:
+            has_user_through_model = False
+
             if model_field.rel:
                 to_many = isinstance(model_field,
                                      models.fields.related.ManyToManyField)
                 related_model = model_field.rel.to
 
+                if to_many and not model_field.rel.through._meta.auto_created:
+                    has_user_through_model = True
+
             if model_field.rel and nested:
                 if len(inspect.getargspec(self.get_nested_field).args) == 2:
                     warnings.warn(
@@ -620,6 +625,9 @@ class ModelSerializer(Serializer):
                 field = self.get_field(model_field)
 
             if field:
+                if has_user_through_model:
+                    field.read_only = True
+
                 ret[model_field.name] = field
 
         # Deal with reverse relationships
@@ -637,6 +645,12 @@ class ModelSerializer(Serializer):
                 continue
             related_model = relation.model
             to_many = relation.field.rel.multiple
+            has_user_through_model = False
+            is_m2m = isinstance(relation.field,
+                                models.fields.related.ManyToManyField)
+
+            if is_m2m and not relation.field.rel.through._meta.auto_created:
+                has_user_through_model = True
 
             if nested:
                 field = self.get_nested_field(None, related_model, to_many)
@@ -644,6 +658,9 @@ class ModelSerializer(Serializer):
                 field = self.get_related_field(None, related_model, to_many)
 
             if field:
+                if has_user_through_model:
+                    field.read_only = True
+
                 ret[accessor_name] = field
 
         # Add the `read_only` flag to any fields that have bee specified
-- 
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