From 8c3f82fb18a58b8e0983612ef3cc35b3c3950b66 Mon Sep 17 00:00:00 2001
From: Susan Dreher
Date: Tue, 27 Jan 2015 16:18:51 -0500
Subject: :bug: ManyRelatedField get_value clearing field on partial update

A PATCH to a serializer's non-related CharField was clearing an ancillary StringRelatedField(many=True) field.
The issue appears to be in the ManyRelatedField's get_value method, which was returning a [] instead of empty
when the request data was a MultiDict.

This fix mirrors code in fields.py, class Field, get_value, Ln. 272, which explicitly returns empty on a partial update.

Tests added to demonstrate the issue.
---
 rest_framework/relations.py | 5 +++++
 1 file changed, 5 insertions(+)

(limited to 'rest_framework')

diff --git a/rest_framework/relations.py b/rest_framework/relations.py
index aa0c2def..13793f37 100644
--- a/rest_framework/relations.py
+++ b/rest_framework/relations.py
@@ -338,7 +338,12 @@ class ManyRelatedField(Field):
         # We override the default field access in order to support
         # lists in HTML forms.
         if html.is_html_input(dictionary):
+            # Don't return [] if the update is partial
+            if self.field_name not in dictionary:
+                if getattr(self.root, 'partial', False):
+                    return empty
             return dictionary.getlist(self.field_name)
+
         return dictionary.get(self.field_name, empty)
 
     def to_internal_value(self, data):
-- 
cgit v1.2.3