lookup_field on hyperlinked fields, and overriddable hyperlinked fields. Closes #688

docs/api-guide/relations.md

@@ -123,9 +123,9 @@ Would serialize to a representation like this:
         'album_name': 'Graceland',
         'artist': 'Paul Simon'
         'tracks': [
-            'http://www.example.com/api/tracks/45',
-            'http://www.example.com/api/tracks/46',
-            'http://www.example.com/api/tracks/47',
+            'http://www.example.com/api/tracks/45/',
+            'http://www.example.com/api/tracks/46/',
+            'http://www.example.com/api/tracks/47/',
             ...
         ]
     }
@@ -138,9 +138,7 @@ By default this field is read-write, although you can change this behavior using
 * `many` - If applied to a to-many relationship, you should set this argument to `True`.
 * `required` - If set to `False`, the field will accept values of `None` or the empty-string for nullable relationships.
 * `queryset` - By default `ModelSerializer` classes will use the default queryset for the relationship.  `Serializer` classes must either set a queryset explicitly, or set `read_only=True`.
-* `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.
 
 ## SlugRelatedField
@@ -196,7 +194,7 @@ Would serialize to a representation like this:
     {
         'album_name': 'The Eraser',
         'artist': 'Thom Yorke'
-        'track_listing': 'http://www.example.com/api/track_list/12',
+        'track_listing': 'http://www.example.com/api/track_list/12/',
     }
  
 This field is always read-only.
@@ -291,32 +289,23 @@ This custom field would then serialize to the following representation.
 
 ## Reverse relations
 
-Note that reverse relationships are not automatically generated by the `ModelSerializer` and `HyperlinkedModelSerializer` classes.  To include a reverse relationship, you cannot simply add it to the fields list.
-
-**The following will not work:**
+Note that reverse relationships are not automatically included by the `ModelSerializer` and `HyperlinkedModelSerializer` classes.  To include a reverse relationship, you must explicitly add it to the fields list.  For example:
 
     class AlbumSerializer(serializers.ModelSerializer):
         class Meta:
-            fields = ('tracks', ...) 
-           
-Instead, you must explicitly add it to the serializer.  For example:
-
-    class AlbumSerializer(serializers.ModelSerializer):
-        tracks = serializers.PrimaryKeyRelatedField(many=True)
-        ...
-
-By default, the field will uses the same accessor as it's field name to retrieve the relationship, so in this example, `Album` instances would need to have the `tracks` attribute for this relationship to work.
+            fields = ('tracks', ...)
 
-The best way to ensure this is typically to make sure that the relationship on the model definition has it's `related_name` argument properly set.  For example:
+You'll normally want to ensure that you've set an appropriate `related_name` argument on the relationship, that you can use as the field name.  For example:
 
     class Track(models.Model):
         album = models.ForeignKey(Album, related_name='tracks')
         ...
 
-Alternatively, you can use the `source` argument on the serializer field, to use a different accessor attribute than the field name.  For example.
+If you have not set a related name for the reverse relationship, you'll need to use the automatically generated related name in the `fields` argument.  For example:
 
     class AlbumSerializer(serializers.ModelSerializer):
-        tracks = serializers.PrimaryKeyRelatedField(many=True, source='track_set')
+        class Meta:
+            fields = ('track_set', ...) 
 
 See the Django documentation on [reverse relationships][reverse-relationships] for more details.
 
@@ -394,6 +383,40 @@ Note that reverse generic keys, expressed using the `GenericRelation` field, can
 
 For more information see [the Django documentation on generic relations][generic-relations].
 
+## Advanced Hyperlinked fields
+
+If you have very specific requirements for the style of your hyperlinked relationships you can override `HyperlinkedRelatedField`. 
+
+There are two methods you'll need to override.
+
+#### get_url(self, obj, view_name, request, format)
+
+This method should return the URL that corresponds to the given object.
+
+May raise a `NoReverseMatch` if the `view_name` and `lookup_field`
+attributes are not configured to correctly match the URL conf.
+
+#### get_object(self, queryset, view_name, view_args, view_kwargs)
+
+
+This method should the object that corresponds to the matched URL conf arguments.
+
+May raise an `ObjectDoesNotExist` exception.
+
+### Example
+
+For example, if all your object URLs used both a account and a slug in the the URL to reference the object, you might create a custom field like this: 
+
+    class CustomHyperlinkedField(serializers.HyperlinkedRelatedField):
+        def get_url(self, obj, view_name, request, format):
+            kwargs = {'account': obj.account, 'slug': obj.slug}
+            return reverse(view_name, kwargs=kwargs, request=request, format=format)
+
+        def get_object(self, queryset, view_name, view_args, view_kwargs):
+            account = view_kwargs['account']
+            slug = view_kwargs['slug']
+            return queryset.get(account=account, slug=sug)
+
 ---
 
 ## Deprecated APIs

rest_framework/relations.py

@@ -288,10 +288,8 @@ class HyperlinkedRelatedField(RelatedField):
     """
     Represents a relationship using hyperlinking.
     """
-    pk_url_kwarg = 'pk'
-    slug_field = 'slug'
-    slug_url_kwarg = None  # Defaults to same as `slug_field` unless overridden
     read_only = False
+    lookup_field = 'pk'
 
     default_error_messages = {
         'no_match': _('Invalid hyperlink - No URL match'),
@@ -301,69 +299,120 @@ class HyperlinkedRelatedField(RelatedField):
         'incorrect_type': _('Incorrect type.  Expected url string, received %s.'),
     }
 
+    # These are all pending deprecation
+    pk_url_kwarg = 'pk'
+    slug_field = 'slug'
+    slug_url_kwarg = None  # Defaults to same as `slug_field` unless overridden
+
     def __init__(self, *args, **kwargs):
         try:
             self.view_name = kwargs.pop('view_name')
         except KeyError:
             raise ValueError("Hyperlinked field requires 'view_name' kwarg")
 
+        self.lookup_field = kwargs.pop('lookup_field', self.lookup_field)
+        self.format = kwargs.pop('format', None)
+
+        # These are pending deprecation
+        self.pk_url_kwarg = kwargs.pop('pk_url_kwarg', self.pk_url_kwarg)
         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)
         self.slug_url_kwarg = kwargs.pop('slug_url_kwarg', default_slug_kwarg)
 
-        self.format = kwargs.pop('format', None)
         super(HyperlinkedRelatedField, self).__init__(*args, **kwargs)
 
-    def get_slug_field(self):
+    def get_url(self, obj, view_name, request, format):
         """
-        Get the name of a slug field to be used to look up by slug.
-        """
-        return self.slug_field
-
-    def to_native(self, obj):
-        view_name = self.view_name
-        request = self.context.get('request', None)
-        format = self.format or self.context.get('format', None)
-
-        if request is None:
-            warnings.warn("Using `HyperlinkedRelatedField` without including the "
-                          "request in the serializer context is deprecated. "
-                          "Add `context={'request': request}` when instantiating the serializer.",
-                          DeprecationWarning, stacklevel=4)
+        Given an object, return the URL that hyperlinks to the object.
 
-        pk = getattr(obj, 'pk', None)
-        if pk is None:
-            return
-        kwargs = {self.pk_url_kwarg: pk}
+        May raise a `NoReverseMatch` if the `view_name` and `lookup_field`
+        attributes are not configured to correctly match the URL conf.
+        """
+        lookup_field = getattr(obj, self.lookup_field)
+        kwargs = {self.lookup_field: lookup_field}
         try:
             return reverse(view_name, kwargs=kwargs, request=request, format=format)
         except NoReverseMatch:
             pass
 
+        if self.pk_url_kwarg != 'pk':
+            # Only try pk if it has been explicitly set.
+            # Otherwise, the default `lookup_field = 'pk'` has us covered.
+            pk = obj.pk
+            kwargs = {self.pk_url_kwarg: pk}
+            try:
+                return reverse(view_name, kwargs=kwargs, request=request, format=format)
+            except NoReverseMatch:
+                pass
+
         slug = getattr(obj, self.slug_field, None)
+        if slug is not None:
+            # Only try slug if it corresponds to an attribute on the object.
+            kwargs = {self.slug_url_kwarg: slug}
+            try:
+                return reverse(view_name, kwargs=kwargs, request=request, format=format)
+            except NoReverseMatch:
+                pass
 
-        if not slug:
-            raise Exception('Could not resolve URL for field using view name "%s"' % view_name)
+        raise NoReverseMatch()
 
-        kwargs = {self.slug_url_kwarg: slug}
-        try:
-            return reverse(view_name, kwargs=kwargs, request=request, format=format)
-        except NoReverseMatch:
-            pass
+    def get_object(self, queryset, view_name, view_args, view_kwargs):
+        """
+        Return the object corresponding to a matched URL.
 
-        kwargs = {self.pk_url_kwarg: obj.pk, self.slug_url_kwarg: slug}
+        Takes the matched URL conf arguments, and the queryset, and should
+        return an object instance, or raise an `ObjectDoesNotExist` exception.
+        """
+        lookup = view_kwargs.get(self.lookup_field, None)
+        pk = view_kwargs.get(self.pk_url_kwarg, None)
+        slug = view_kwargs.get(self.slug_url_kwarg, None)
+
+        if lookup is not None:
+            filter_kwargs = {self.lookup_field: lookup}
+        elif pk is not None:
+            filter_kwargs = {'pk': pk}
+        elif slug is not None:
+            filter_kwargs = {self.slug_field: slug}
+        else:
+            raise ObjectDoesNotExist()
+
+        return queryset.get(**filter_kwargs)
+
+    def to_native(self, obj):
+        view_name = self.view_name
+        request = self.context.get('request', None)
+        format = self.format or self.context.get('format', None)
+
+        if request is None:
+            msg = (
+                "Using `HyperlinkedRelatedField` without including the request "
+                "in the serializer context is deprecated. "
+                "Add `context={'request': request}` when instantiating "
+                "the serializer."
+            )
+            warnings.warn(msg, DeprecationWarning, stacklevel=4)
+
+        # If the object has not yet been saved then we cannot hyperlink to it.
+        if getattr(obj, 'pk', None) is None:
+            return
+
+        # Return the hyperlink, or error if incorrectly configured.
         try:
-            return reverse(view_name, kwargs=kwargs, request=request, format=format)
+            return self.get_url(obj, view_name, request, format)
         except NoReverseMatch:
-            pass
-
-        raise Exception('Could not resolve URL for field using view name "%s"' % view_name)
+            msg = (
+                'Could not resolve URL for hyperlinked relationship using '
+                'view name "%s". You may have failed to include the related '
+                'model in your API, or incorrectly configured the '
+                '`lookup_field` attribute on this field.'
+            )
+            raise Exception(msg % view_name)
 
     def from_native(self, value):
         # Convert URL -> model instance pk
         # TODO: Use values_list
-        if self.queryset is None:
+        queryset = self.queryset
+        if queryset is None:
             raise Exception('Writable related fields must include a `queryset` argument')
 
         try:
@@ -387,29 +436,11 @@ class HyperlinkedRelatedField(RelatedField):
         if match.view_name != self.view_name:
             raise ValidationError(self.error_messages['incorrect_match'])
 
-        pk = match.kwargs.get(self.pk_url_kwarg, None)
-        slug = match.kwargs.get(self.slug_url_kwarg, None)
-
-        # Try explicit primary key.
-        if pk is not None:
-            queryset = self.queryset.filter(pk=pk)
-        # Next, try looking up by slug.
-        elif slug is not None:
-            slug_field = self.get_slug_field()
-            queryset = self.queryset.filter(**{slug_field: slug})
-        # If none of those are defined, it's probably a configuation error.
-        else:
-            raise ValidationError(self.error_messages['configuration_error'])
-
         try:
-            obj = queryset.get()
-        except ObjectDoesNotExist:
+            return self.get_object(queryset, match.view_name,
+                                   match.args, match.kwargs)
+        except (ObjectDoesNotExist, TypeError, ValueError):
             raise ValidationError(self.error_messages['does_not_exist'])
-        except (TypeError, ValueError):
-            msg = self.error_messages['incorrect_type']
-            raise ValidationError(msg % type(value).__name__)
-
-        return obj
 
 
 class HyperlinkedIdentityField(Field):

rest_framework/serializers.py

@@ -836,6 +836,7 @@ class HyperlinkedModelSerializer(ModelSerializer):
     """
     _options_class = HyperlinkedModelSerializerOptions
     _default_view_name = '%(model_name)s-detail'
+    _hyperlink_field_class = HyperlinkedRelatedField
 
     url = HyperlinkedIdentityField()
 
@@ -874,7 +875,7 @@ class HyperlinkedModelSerializer(ModelSerializer):
         if model_field:
             kwargs['required'] = not(model_field.null or model_field.blank)
 
-        return HyperlinkedRelatedField(**kwargs)
+        return self._hyperlink_field_class(**kwargs)
 
     def get_identity(self, data):
         """