HyperlinkedIdentityField uses lookup_field kwarg.

According to the [Serializers API Guide][1], `HyperlinkedIdentityField`
takes `lookup_field` as a kwarg like the other related fields and the
generic views. However, this was not actually implemented.

[1]: http://django-rest-framework.org/api-guide/serializers.html#hyperlinkedmodelserializer

docs/api-guide/relations.md

@@ -196,15 +196,13 @@ Would serialize to a representation like this:
         'artist': 'Thom Yorke'
         'track_listing': 'http://www.example.com/api/track_list/12/',
     }
- 
+
 This field is always read-only.
 
 **Arguments**:
 
 * `view_name` - The view name that should be used as the target of the relationship.  **required**.
-* `slug_field` - The field on the target that should be used for the lookup. Default is `'slug'`.
-* `pk_url_kwarg` - The named url parameter for the pk field lookup. Default is `pk`.
-* `slug_url_kwarg` - The named url parameter for the slug field lookup. Default is to use the same value as given for `slug_field`.
+* `lookup_field` - The field on the target that should be used for the lookup.  Should correspond to a URL keyword argument on the referenced view. Default is `'pk'`.
 * `format` - If using format suffixes, hyperlinked fields will use the same format suffix for the target unless overridden by using the `format` argument.
 
 ---

rest_framework/relations.py

@@ -465,10 +465,13 @@ class HyperlinkedIdentityField(Field):
     """
     Represents the instance, or a property on the instance, using hyperlinking.
     """
+    lookup_field = 'pk'
+    read_only = True
+
+    # These are all pending deprecation
     pk_url_kwarg = 'pk'
     slug_field = 'slug'
     slug_url_kwarg = None  # Defaults to same as `slug_field` unless overridden
-    read_only = True
 
     def __init__(self, *args, **kwargs):
         # TODO: Make view_name mandatory, and have the
@@ -477,6 +480,19 @@ class HyperlinkedIdentityField(Field):
         # Optionally the format of the target hyperlink may be specified
         self.format = kwargs.pop('format', None)
 
+        self.lookup_field = kwargs.pop('lookup_field', self.lookup_field)
+
+        # These are pending deprecation
+        if 'pk_url_kwarg' in kwargs:
+            msg = 'pk_url_kwarg is pending deprecation. Use lookup_field instead.'
+            warnings.warn(msg, PendingDeprecationWarning, stacklevel=2)
+        if 'slug_url_kwarg' in kwargs:
+            msg = 'slug_url_kwarg is pending deprecation. Use lookup_field instead.'
+            warnings.warn(msg, PendingDeprecationWarning, stacklevel=2)
+        if 'slug_field' in kwargs:
+            msg = 'slug_field is pending deprecation. Use lookup_field instead.'
+            warnings.warn(msg, PendingDeprecationWarning, stacklevel=2)
+
         self.slug_field = kwargs.pop('slug_field', self.slug_field)
         default_slug_kwarg = self.slug_url_kwarg or self.slug_field
         self.pk_url_kwarg = kwargs.pop('pk_url_kwarg', self.pk_url_kwarg)
@@ -488,7 +504,8 @@ class HyperlinkedIdentityField(Field):
         request = self.context.get('request', None)
         format = self.context.get('format', None)
         view_name = self.view_name or self.parent.opts.view_name
-        kwargs = {self.pk_url_kwarg: obj.pk}
+        lookup_field = getattr(obj, self.lookup_field)
+        kwargs = {self.lookup_field: lookup_field}
 
         if request is None:
             warnings.warn("Using `HyperlinkedIdentityField` without including the "

rest_framework/tests/hyperlinkedserializers.py

@@ -27,6 +27,14 @@ class PhotoSerializer(serializers.Serializer):
         return Photo(**attrs)
 
 
+class AlbumSerializer(serializers.ModelSerializer):
+    url = serializers.HyperlinkedIdentityField(view_name='album-detail', lookup_field='title')
+
+    class Meta:
+        model = Album
+        fields = ('title', 'url')
+
+
 class BasicList(generics.ListCreateAPIView):
     model = BasicModel
     model_serializer_class = serializers.HyperlinkedModelSerializer
@@ -73,6 +81,8 @@ class PhotoListCreate(generics.ListCreateAPIView):
 
 class AlbumDetail(generics.RetrieveAPIView):
     model = Album
+    serializer_class = AlbumSerializer
+    lookup_field = 'title'
 
 
 class OptionalRelationDetail(generics.RetrieveUpdateDestroyAPIView):
@@ -180,6 +190,36 @@ class TestManyToManyHyperlinkedView(TestCase):
         self.assertEqual(response.data, self.data[0])
 
 
+class TestHyperlinkedIdentityFieldLookup(TestCase):
+    urls = 'rest_framework.tests.hyperlinkedserializers'
+
+    def setUp(self):
+        """
+        Create 3 Album instances.
+        """
+        titles = ['foo', 'bar', 'baz']
+        for title in titles:
+            album = Album(title=title)
+            album.save()
+        self.detail_view = AlbumDetail.as_view()
+        self.data = {
+            'foo': {'title': 'foo', 'url': 'http://testserver/albums/foo/'},
+            'bar': {'title': 'bar', 'url': 'http://testserver/albums/bar/'},
+            'baz': {'title': 'baz', 'url': 'http://testserver/albums/baz/'}
+        }
+
+    def test_lookup_field(self):
+        """
+        GET requests to AlbumDetail view should return serialized Albums
+        with a url field keyed by `title`.
+        """
+        for album in Album.objects.all():
+            request = factory.get('/albums/{0}/'.format(album.title))
+            response = self.detail_view(request, title=album.title)
+            self.assertEqual(response.status_code, status.HTTP_200_OK)
+            self.assertEqual(response.data, self.data[album.title])
+
+
 class TestCreateWithForeignKeys(TestCase):
     urls = 'rest_framework.tests.hyperlinkedserializers'