From 2c83fc51a69396d72e5ebe2630c4c54c79dc5048 Mon Sep 17 00:00:00 2001
From: Kevin Vance <kvance@kvance.com>
Date: Thu, 16 Jun 2016 15:44:33 -0400
Subject: [PATCH] Lazily get the name of hyperlinked models

Add support for Hyperlink names to be callable.  This allows the call
to get_name() in HyperlinkedRelatedField to be deferred until the
property is accessed.
---
 rest_framework/relations.py | 18 +++++++++++++++---
 tests/test_relations.py     | 12 ++++++++++++
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/rest_framework/relations.py b/rest_framework/relations.py
index 2e7c51b22..2d7508418 100644
--- a/rest_framework/relations.py
+++ b/rest_framework/relations.py
@@ -35,15 +35,27 @@ class Hyperlink(six.text_type):
     A string like object that additionally has an associated name.
     We use this for hyperlinked URLs that may render as a named link
     in some contexts, or render as a plain URL in others.
+
+    If name is callable, it will be called when the name property is
+    accessed.
     """
     def __new__(self, url, name):
         ret = six.text_type.__new__(self, url)
-        ret.name = name
+        if callable(name):
+            ret._name_callable = name
+        else:
+            ret.name = name
         return ret
 
     def __getnewargs__(self):
         return(str(self), self.name,)
 
+    def __getattr__(self, key):
+        if key == 'name' and hasattr(self, '_name_callable'):
+            f = getattr(self, '_name_callable')
+            return f()
+        raise AttributeError
+
     is_hyperlink = True
 
 
@@ -368,8 +380,8 @@ class HyperlinkedRelatedField(RelatedField):
         if url is None:
             return None
 
-        name = self.get_name(value)
-        return Hyperlink(url, name)
+        name_getter = lambda: self.get_name(value)
+        return Hyperlink(url, name_getter)
 
 
 class HyperlinkedIdentityField(HyperlinkedRelatedField):
diff --git a/tests/test_relations.py b/tests/test_relations.py
index a070ad6de..edf955b20 100644
--- a/tests/test_relations.py
+++ b/tests/test_relations.py
@@ -98,6 +98,11 @@ class TestHyperlinkedRelatedField(APISimpleTestCase):
         representation = self.field.to_representation(MockObject(pk=''))
         assert representation is None
 
+    def test_representation_does_not_call_get_name(self):
+        self.field.get_name = lambda _: pytest.fail(
+            "HyperlinkedRelatedField.get_name() called eagerly")
+        self.field.to_representation(MockObject(pk=1))
+
 
 class TestHyperlinkedIdentityField(APISimpleTestCase):
     def setUp(self):
@@ -233,9 +238,16 @@ class TestManyRelatedField(APISimpleTestCase):
 class TestHyperlink:
     def setup(self):
         self.default_hyperlink = serializers.Hyperlink('http://example.com', 'test')
+        self.callable_hyperlink = serializers.Hyperlink('http://example.com', lambda: 'called')
 
     def test_can_be_pickled(self):
         import pickle
         upkled = pickle.loads(pickle.dumps(self.default_hyperlink))
         assert upkled == self.default_hyperlink
         assert upkled.name == self.default_hyperlink.name
+
+    def test_simple_name_property(self):
+        assert 'test' == self.default_hyperlink.name
+
+    def test_callable_name_property(self):
+        assert 'called' == self.callable_hyperlink.name