Set up serializer fields lazily on-demand.

This avoids AppRegistryNotReady problems in Django 1.7 with nested serializers,
which are instantiated at import time, possibly before Django's app registry is
fully populated.

1 files changed, 5 insertions, 1 deletions

diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index b3db3582..340c6be0 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -22,6 +22,7 @@ from django.db import models
 from django.forms import widgets
 from django.utils import six
 from django.utils.datastructures import SortedDict
+from django.utils.functional import cached_property
 from django.core.exceptions import ObjectDoesNotExist
 from rest_framework.settings import api_settings
 
@@ -197,7 +198,6 @@ class BaseSerializer(WritableField):
         self.init_data = data
         self.init_files = files
         self.object = instance
-        self.fields = self.get_fields()
 
         self._data = None
         self._files = None
@@ -212,6 +212,10 @@ class BaseSerializer(WritableField):
     #####
     # Methods to determine which fields to use when (de)serializing objects.
 
+    @cached_property
+    def fields(self):
+        return self.get_fields()
+
     def get_default_fields(self):
         """
         Return the complete set of default fields for the object, as a dict.