From fb58ef043cc39d900bb8389855f07087cb0d7920 Mon Sep 17 00:00:00 2001
From: Matt d'Entremont
Date: Wed, 4 Mar 2015 17:36:03 -0400
Subject: Add support for serializing models with m2m related fields

- In both ManyRelatedField, provide an empty return when trying to
  access a relation field if the instance in question has no PK (so
  likely hasn't been inserted yet)
- Add relevant tests
- Without these changes, exceptions would be raised when trying to
  serialize the uncreated models as it is impossible to query
  relations without a PK
- Add test to ensure RelatedField does not regress as currently 
  supports being serialized with and unsaved model---
 rest_framework/relations.py | 4 ++++
 1 file changed, 4 insertions(+)

(limited to 'rest_framework')

diff --git a/rest_framework/relations.py b/rest_framework/relations.py
index 0b7c9d86..3a966c5b 100644
--- a/rest_framework/relations.py
+++ b/rest_framework/relations.py
@@ -360,6 +360,10 @@ class ManyRelatedField(Field):
         ]
 
     def get_attribute(self, instance):
+        # Can't have any relationships if not created
+        if not instance.pk:
+            return []
+
         relationship = get_attribute(instance, self.source_attrs)
         return relationship.all() if (hasattr(relationship, 'all')) else relationship
 
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