7 files changed, 617 insertions, 595 deletions

diff --git a/docs/api-guide/fields.md b/docs/api-guide/fields.md
index 50a09701..5bc8f7f7 100644
--- a/docs/api-guide/fields.md
+++ b/docs/api-guide/fields.md
@@ -2,11 +2,11 @@
 
 # Serializer fields
 
-> Flat is better than nested.
+> Each field in a Form class is responsible not only for validating data, but also for "cleaning" it -- normalizing it to a consistent format. 
 >
-> — [The Zen of Python][cite]
+> — [Django documentation][cite]
 
-Serializer fields handle converting between primative values and internal datatypes.  They also deal with validating input values, as well as retrieving and setting the values from their parent objects.
+Serializer fields handle converting between primitive values and internal datatypes.  They also deal with validating input values, as well as retrieving and setting the values from their parent objects.
 
 ---
 
@@ -28,7 +28,7 @@ Defaults to the name of the field.
 
 ### `read_only`
 
-Set this to `True` to ensure that the field is used when serializing a representation, but is not used when updating an instance dureing deserialization.
+Set this to `True` to ensure that the field is used when serializing a representation, but is not used when updating an instance during deserialization.
 
 Defaults to `False`
 
@@ -41,7 +41,7 @@ Defaults to `True`.
 
 ### `default`
 
-If set, this gives the default value that will be used for the field if none is supplied.  If not set the default behaviour is to not populate the attribute at all.
+If set, this gives the default value that will be used for the field if none is supplied.  If not set the default behavior is to not populate the attribute at all.
 
 ### `validators`
 
@@ -96,9 +96,9 @@ Would produce output similar to:
         'expired': True
     }
 
-By default, the `Field` class will perform a basic translation of the source value into primative datatypes, falling back to unicode representations of complex datatypes when necessary.
+By default, the `Field` class will perform a basic translation of the source value into primitive datatypes, falling back to unicode representations of complex datatypes when necessary.
 
-You can customize this  behaviour by overriding the `.to_native(self, value)` method.
+You can customize this  behavior by overriding the `.to_native(self, value)` method.
 
 ## WritableField
 
@@ -110,6 +110,24 @@ A generic field that can be tied to any arbitrary model field.  The `ModelField`
 
 **Signature:** `ModelField(model_field=<Django ModelField class>)`
 
+## SerializerMethodField
+
+This is a read-only field. It gets its value by calling a method on the serializer class it is attached to. It can be used to add any sort of data to the serialized representation of your object. The field's constructor accepts a single argument, which is the name of the method on the serializer to be called. The method should accept a single argument (in addition to `self`), which is the object being serialized. It should return whatever you want to be included in the serialized representation of the object. For example:
+
+    from rest_framework import serializers
+    from django.contrib.auth.models import User
+    from django.utils.timezone import now
+
+    class UserSerializer(serializers.ModelSerializer):
+
+        days_since_joined = serializers.SerializerMethodField('get_days_since_joined')
+
+        class Meta:
+            model = User
+
+        def get_days_since_joined(self, obj):
+            return (now() - obj.date_joined).days
+
 ---
 
 # Typed Fields
@@ -211,151 +229,8 @@ Signature and validation is the same as with `FileField`.
 
 ---
 
-**Note:** `FileFields` and `ImageFields` are only suitable for use with MultiPartParser, since eg json doesn't support file uploads.
+**Note:** `FileFields` and `ImageFields` are only suitable for use with MultiPartParser, since e.g. json doesn't support file uploads.
 Django's regular [FILE_UPLOAD_HANDLERS] are used for handling uploaded files. 
 
----
-
-# Relational Fields
-
-Relational fields are used to represent model relationships.  They can be applied to `ForeignKey`, `ManyToManyField` and `OneToOneField` relationships, as well as to reverse relationships, and custom relationships such as `GenericForeignKey`.
-
-## RelatedField
-
-This field can be applied to any of the following:
-
-* A `ForeignKey` field.
-* A `OneToOneField` field.
-* A reverse OneToOne relationship
-* Any other "to-one" relationship.
-
-By default `RelatedField` will represent the target of the field using it's `__unicode__` method.
-
-You can customise this behaviour by subclassing `ManyRelatedField`, and overriding the `.to_native(self, value)` method.
-
-## ManyRelatedField
-
-This field can be applied to any of the following:
- 
-* A `ManyToManyField` field.
-* A reverse ManyToMany relationship.
-* A reverse ForeignKey relationship
-* Any other "to-many" relationship.
-
-By default `ManyRelatedField` will represent the targets of the field using their `__unicode__` method.
-
-For example, given the following models:
-
-    class TaggedItem(models.Model):
-        """
-        Tags arbitrary model instances using a generic relation.
-        
-        See: https://docs.djangoproject.com/en/dev/ref/contrib/contenttypes/
-        """
-        tag = models.SlugField()
-        content_type = models.ForeignKey(ContentType)
-        object_id = models.PositiveIntegerField()
-        content_object = GenericForeignKey('content_type', 'object_id')
-    
-        def __unicode__(self):
-            return self.tag
-    
-    
-    class Bookmark(models.Model):
-        """
-        A bookmark consists of a URL, and 0 or more descriptive tags.
-        """
-        url = models.URLField()
-        tags = GenericRelation(TaggedItem)
-
-And a model serializer defined like this:
-
-    class BookmarkSerializer(serializers.ModelSerializer):
-        tags = serializers.ManyRelatedField(source='tags')
-
-        class Meta:
-            model = Bookmark
-            exclude = ('id',)
-
-Then an example output format for a Bookmark instance would be:
-
-    {
-        'tags': [u'django', u'python'],
-        'url': u'https://www.djangoproject.com/'
-    }
-
-## PrimaryKeyRelatedField / ManyPrimaryKeyRelatedField
-
-`PrimaryKeyRelatedField` and `ManyPrimaryKeyRelatedField` will represent the target of the relationship using it's primary key.
-
-By default these fields are read-write, although you can change this behaviour using the `read_only` flag.
-
-**Arguments**:
-
-* `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`.
-* `null` - If set to `True`, the field will accept values of `None` or the emptystring for nullable relationships.
-
-## SlugRelatedField / ManySlugRelatedField
-
-`SlugRelatedField` and `ManySlugRelatedField` will represent the target of the relationship using a unique slug.
-
-By default these fields read-write, although you can change this behaviour using the `read_only` flag.
-
-**Arguments**:
-
-* `slug_field` - The field on the target that should be used to represent it.  This should be a field that uniquely identifies any given instance.  For example, `username`.
-* `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`.
-* `null` - If set to `True`, the field will accept values of `None` or the emptystring for nullable relationships.
-
-## HyperlinkedRelatedField / ManyHyperlinkedRelatedField
-
-`HyperlinkedRelatedField` and `ManyHyperlinkedRelatedField` will represent the target of the relationship using a hyperlink.
-
-By default, `HyperlinkedRelatedField` is read-write, although you can change this behaviour using the `read_only` flag.
-
-**Arguments**:
-
-* `view_name` - The view name that should be used as the target of the relationship.  **required**.
-* `format` - If using format suffixes, hyperlinked fields will use the same format suffix for the target unless overridden by using the `format` argument.
-* `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`.
-* `null` - If set to `True`, the field will accept values of `None` or the emptystring for nullable relationships.
-
-## HyperLinkedIdentityField
-
-This field can be applied as an identity relationship, such as the `'url'` field on  a HyperlinkedModelSerializer.
-
-This field is always read-only.
-
-**Arguments**:
-
-* `view_name` - The view name that should be used as the target of the relationship.  **required**.
-* `format` - If using format suffixes, hyperlinked fields will use the same format suffix for the target unless overridden by using the `format` argument.
-* `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`.
-
-# Other Fields
-
-## SerializerMethodField
-
-This is a read-only field. It gets its value by calling a method on the serializer class it is attached to. It can be used to add any sort of data to the serialized representation of your object. The field's constructor accepts a single argument, which is the name of the method on the serializer to be called. The method should accept a single argument (in addition to `self`), which is the object being serialized. It should return whatever you want to be included in the serialized representation of the object. For example:
-
-    from rest_framework import serializers
-    from django.contrib.auth.models import User
-    from django.utils.timezone import now
-
-    class UserSerializer(serializers.ModelSerializer):
-
-        days_since_joined = serializers.SerializerMethodField('get_days_since_joined')
-
-        class Meta:
-            model = User
-
-        def get_days_since_joined(self, obj):
-            return (now() - obj.date_joined).days
-
-[cite]: http://www.python.org/dev/peps/pep-0020/
+[cite]: https://docs.djangoproject.com/en/dev/ref/forms/api/#django.forms.Form.cleaned_data
 [FILE_UPLOAD_HANDLERS]: https://docs.djangoproject.com/en/dev/ref/settings/#std:setting-FILE_UPLOAD_HANDLERS
diff --git a/docs/api-guide/relations.md b/docs/api-guide/relations.md
new file mode 100644
index 00000000..351b5e09
--- /dev/null
+++ b/docs/api-guide/relations.md
@@ -0,0 +1,139 @@
+<a class="github" href="relations.py"></a>
+
+# Serializer relations
+
+> Bad programmers worry about the code.
+> Good programmers worry about data structures and their relationships.
+>
+> &mdash; [Linus Torvalds][cite]
+
+
+Relational fields are used to represent model relationships.  They can be applied to `ForeignKey`, `ManyToManyField` and `OneToOneField` relationships, as well as to reverse relationships, and custom relationships such as `GenericForeignKey`.
+
+---
+
+**Note:** The relational fields are declared in `relations.py`, but by convention you should import them using `from rest_framework import serializers` and refer to fields as `serializers.<FieldName>`.
+
+---
+
+## RelatedField
+
+This field can be applied to any of the following:
+
+* A `ForeignKey` field.
+* A `OneToOneField` field.
+* A reverse OneToOne relationship
+* Any other "to-one" relationship.
+
+By default `RelatedField` will represent the target of the field using it's `__unicode__` method.
+
+You can customize this behavior by subclassing `ManyRelatedField`, and overriding the `.to_native(self, value)` method.
+
+## ManyRelatedField
+
+This field can be applied to any of the following:
+ 
+* A `ManyToManyField` field.
+* A reverse ManyToMany relationship.
+* A reverse ForeignKey relationship
+* Any other "to-many" relationship.
+
+By default `ManyRelatedField` will represent the targets of the field using their `__unicode__` method.
+
+For example, given the following models:
+
+    class TaggedItem(models.Model):
+        """
+        Tags arbitrary model instances using a generic relation.
+        
+        See: https://docs.djangoproject.com/en/dev/ref/contrib/contenttypes/
+        """
+        tag = models.SlugField()
+        content_type = models.ForeignKey(ContentType)
+        object_id = models.PositiveIntegerField()
+        content_object = GenericForeignKey('content_type', 'object_id')
+    
+        def __unicode__(self):
+            return self.tag
+    
+    
+    class Bookmark(models.Model):
+        """
+        A bookmark consists of a URL, and 0 or more descriptive tags.
+        """
+        url = models.URLField()
+        tags = GenericRelation(TaggedItem)
+
+And a model serializer defined like this:
+
+    class BookmarkSerializer(serializers.ModelSerializer):
+        tags = serializers.ManyRelatedField(source='tags')
+
+        class Meta:
+            model = Bookmark
+            exclude = ('id',)
+
+Then an example output format for a Bookmark instance would be:
+
+    {
+        'tags': [u'django', u'python'],
+        'url': u'https://www.djangoproject.com/'
+    }
+
+## PrimaryKeyRelatedField
+## ManyPrimaryKeyRelatedField
+
+`PrimaryKeyRelatedField` and `ManyPrimaryKeyRelatedField` will represent the target of the relationship using it's primary key.
+
+By default these fields are read-write, although you can change this behavior using the `read_only` flag.
+
+**Arguments**:
+
+* `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`.
+* `null` - If set to `True`, the field will accept values of `None` or the empty-string for nullable relationships.
+
+## SlugRelatedField
+## ManySlugRelatedField
+
+`SlugRelatedField` and `ManySlugRelatedField` will represent the target of the relationship using a unique slug.
+
+By default these fields read-write, although you can change this behavior using the `read_only` flag.
+
+**Arguments**:
+
+* `slug_field` - The field on the target that should be used to represent it.  This should be a field that uniquely identifies any given instance.  For example, `username`.
+* `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`.
+* `null` - If set to `True`, the field will accept values of `None` or the empty-string for nullable relationships.
+
+## HyperlinkedRelatedField
+## ManyHyperlinkedRelatedField
+
+`HyperlinkedRelatedField` and `ManyHyperlinkedRelatedField` will represent the target of the relationship using a hyperlink.
+
+By default, `HyperlinkedRelatedField` is read-write, although you can change this behavior using the `read_only` flag.
+
+**Arguments**:
+
+* `view_name` - The view name that should be used as the target of the relationship.  **required**.
+* `format` - If using format suffixes, hyperlinked fields will use the same format suffix for the target unless overridden by using the `format` argument.
+* `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`.
+* `null` - If set to `True`, the field will accept values of `None` or the empty-string for nullable relationships.
+
+## HyperLinkedIdentityField
+
+This field can be applied as an identity relationship, such as the `'url'` field on  a HyperlinkedModelSerializer.
+
+This field is always read-only.
+
+**Arguments**:
+
+* `view_name` - The view name that should be used as the target of the relationship.  **required**.
+* `format` - If using format suffixes, hyperlinked fields will use the same format suffix for the target unless overridden by using the `format` argument.
+* `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`.
+
+[cite]: http://lwn.net/Articles/193245/
diff --git a/docs/index.md b/docs/index.md
index 69d972d0..4d50e5d6 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -94,6 +94,7 @@ The API guide is your complete reference manual to all the functionality provide
 * [Renderers][renderers]
 * [Serializers][serializers]
 * [Serializer fields][fields]
+* [Serializer relations][relations]
 * [Authentication][authentication]
 * [Permissions][permissions]
 * [Throttling][throttling]
@@ -185,6 +186,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 [renderers]: api-guide/renderers.md
 [serializers]: api-guide/serializers.md
 [fields]: api-guide/fields.md
+[relations]: api-guide/relations.md
 [authentication]: api-guide/authentication.md
 [permissions]: api-guide/permissions.md
 [throttling]: api-guide/throttling.md
diff --git a/docs/template.html b/docs/template.html
index 676a4807..d789cc58 100644
--- a/docs/template.html
+++ b/docs/template.html
@@ -72,6 +72,7 @@
                   <li><a href="{{ base_url }}/api-guide/renderers{{ suffix }}">Renderers</a></li>
                   <li><a href="{{ base_url }}/api-guide/serializers{{ suffix }}">Serializers</a></li>
                   <li><a href="{{ base_url }}/api-guide/fields{{ suffix }}">Serializer fields</a></li>
+                  <li><a href="{{ base_url }}/api-guide/relations{{ suffix }}">Serializer relations</a></li>
                   <li><a href="{{ base_url }}/api-guide/authentication{{ suffix }}">Authentication</a></li>
                   <li><a href="{{ base_url }}/api-guide/permissions{{ suffix }}">Permissions</a></li>
                   <li><a href="{{ base_url }}/api-guide/throttling{{ suffix }}">Throttling</a></li>
diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index dd90c3f8..d8b82e5f 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -7,18 +7,14 @@ import warnings
 from io import BytesIO
 
 from django.core import validators
-from django.core.exceptions import ObjectDoesNotExist, ValidationError
-from django.core.urlresolvers import resolve, get_script_prefix
+from django.core.exceptions import ValidationError
 from django.conf import settings
 from django import forms
 from django.forms import widgets
-from django.forms.models import ModelChoiceIterator
 from django.utils.encoding import is_protected_type, smart_unicode
 from django.utils.translation import ugettext_lazy as _
-from rest_framework.reverse import reverse
 from rest_framework.compat import parse_date, parse_datetime
 from rest_framework.compat import timezone
-from urlparse import urlparse
 
 
 def is_simple_callable(obj):
@@ -252,443 +248,6 @@ class ModelField(WritableField):
             "type": self.model_field.get_internal_type()
         }
 
-##### Relational fields #####
-
-
-# Not actually Writable, but subclasses may need to be.
-class RelatedField(WritableField):
-    """
-    Base class for related model fields.
-
-    If not overridden, this represents a to-one relationship, using the unicode
-    representation of the target.
-    """
-    widget = widgets.Select
-    cache_choices = False
-    empty_label = None
-    default_read_only = True  # TODO: Remove this
-
-    def __init__(self, *args, **kwargs):
-        self.queryset = kwargs.pop('queryset', None)
-        self.null = kwargs.pop('null', False)
-        super(RelatedField, self).__init__(*args, **kwargs)
-        self.read_only = kwargs.pop('read_only', self.default_read_only)
-
-    def initialize(self, parent, field_name):
-        super(RelatedField, self).initialize(parent, field_name)
-        if self.queryset is None and not self.read_only:
-            try:
-                manager = getattr(self.parent.opts.model, self.source or field_name)
-                if hasattr(manager, 'related'):  # Forward
-                    self.queryset = manager.related.model._default_manager.all()
-                else:  # Reverse
-                    self.queryset = manager.field.rel.to._default_manager.all()
-            except:
-                raise
-                msg = ('Serializer related fields must include a `queryset`' +
-                       ' argument or set `read_only=True')
-                raise Exception(msg)
-
-    ### We need this stuff to make form choices work...
-
-    # def __deepcopy__(self, memo):
-    #     result = super(RelatedField, self).__deepcopy__(memo)
-    #     result.queryset = result.queryset
-    #     return result
-
-    def prepare_value(self, obj):
-        return self.to_native(obj)
-
-    def label_from_instance(self, obj):
-        """
-        Return a readable representation for use with eg. select widgets.
-        """
-        desc = smart_unicode(obj)
-        ident = smart_unicode(self.to_native(obj))
-        if desc == ident:
-            return desc
-        return "%s - %s" % (desc, ident)
-
-    def _get_queryset(self):
-        return self._queryset
-
-    def _set_queryset(self, queryset):
-        self._queryset = queryset
-        self.widget.choices = self.choices
-
-    queryset = property(_get_queryset, _set_queryset)
-
-    def _get_choices(self):
-        # If self._choices is set, then somebody must have manually set
-        # the property self.choices. In this case, just return self._choices.
-        if hasattr(self, '_choices'):
-            return self._choices
-
-        # Otherwise, execute the QuerySet in self.queryset to determine the
-        # choices dynamically. Return a fresh ModelChoiceIterator that has not been
-        # consumed. Note that we're instantiating a new ModelChoiceIterator *each*
-        # time _get_choices() is called (and, thus, each time self.choices is
-        # accessed) so that we can ensure the QuerySet has not been consumed. This
-        # construct might look complicated but it allows for lazy evaluation of
-        # the queryset.
-        return ModelChoiceIterator(self)
-
-    def _set_choices(self, value):
-        # Setting choices also sets the choices on the widget.
-        # choices can be any iterable, but we call list() on it because
-        # it will be consumed more than once.
-        self._choices = self.widget.choices = list(value)
-
-    choices = property(_get_choices, _set_choices)
-
-    ### Regular serializer stuff...
-
-    def field_to_native(self, obj, field_name):
-        value = getattr(obj, self.source or field_name)
-        return self.to_native(value)
-
-    def field_from_native(self, data, files, field_name, into):
-        if self.read_only:
-            return
-
-        try:
-            value = data[field_name]
-        except KeyError:
-            if self.required:
-                raise ValidationError(self.error_messages['required'])
-            return
-
-        if value in (None, '') and not self.null:
-            raise ValidationError('Value may not be null')
-        elif value in (None, '') and self.null:
-            into[(self.source or field_name)] = None
-        else:
-            into[(self.source or field_name)] = self.from_native(value)
-
-
-class ManyRelatedMixin(object):
-    """
-    Mixin to convert a related field to a many related field.
-    """
-    widget = widgets.SelectMultiple
-
-    def field_to_native(self, obj, field_name):
-        value = getattr(obj, self.source or field_name)
-        return [self.to_native(item) for item in value.all()]
-
-    def field_from_native(self, data, files, field_name, into):
-        if self.read_only:
-            return
-
-        try:
-            # Form data
-            value = data.getlist(self.source or field_name)
-        except:
-            # Non-form data
-            value = data.get(self.source or field_name)
-        else:
-            if value == ['']:
-                value = []
-
-        into[field_name] = [self.from_native(item) for item in value]
-
-
-class ManyRelatedField(ManyRelatedMixin, RelatedField):
-    """
-    Base class for related model managers.
-
-    If not overridden, this represents a to-many relationship, using the unicode
-    representations of the target, and is read-only.
-    """
-    pass
-
-
-### PrimaryKey relationships
-
-class PrimaryKeyRelatedField(RelatedField):
-    """
-    Represents a to-one relationship as a pk value.
-    """
-    default_read_only = False
-    form_field_class = forms.ChoiceField
-
-    # TODO: Remove these field hacks...
-    def prepare_value(self, obj):
-        return self.to_native(obj.pk)
-
-    def label_from_instance(self, obj):
-        """
-        Return a readable representation for use with eg. select widgets.
-        """
-        desc = smart_unicode(obj)
-        ident = smart_unicode(self.to_native(obj.pk))
-        if desc == ident:
-            return desc
-        return "%s - %s" % (desc, ident)
-
-    # TODO: Possibly change this to just take `obj`, through prob less performant
-    def to_native(self, pk):
-        return pk
-
-    def from_native(self, data):
-        if self.queryset is None:
-            raise Exception('Writable related fields must include a `queryset` argument')
-
-        try:
-            return self.queryset.get(pk=data)
-        except ObjectDoesNotExist:
-            msg = "Invalid pk '%s' - object does not exist." % smart_unicode(data)
-            raise ValidationError(msg)
-
-    def field_to_native(self, obj, field_name):
-        try:
-            # Prefer obj.serializable_value for performance reasons
-            pk = obj.serializable_value(self.source or field_name)
-        except AttributeError:
-            # RelatedObject (reverse relationship)
-            obj = getattr(obj, self.source or field_name)
-            return self.to_native(obj.pk)
-        # Forward relationship
-        return self.to_native(pk)
-
-
-class ManyPrimaryKeyRelatedField(ManyRelatedField):
-    """
-    Represents a to-many relationship as a pk value.
-    """
-    default_read_only = False
-    form_field_class = forms.MultipleChoiceField
-
-    def prepare_value(self, obj):
-        return self.to_native(obj.pk)
-
-    def label_from_instance(self, obj):
-        """
-        Return a readable representation for use with eg. select widgets.
-        """
-        desc = smart_unicode(obj)
-        ident = smart_unicode(self.to_native(obj.pk))
-        if desc == ident:
-            return desc
-        return "%s - %s" % (desc, ident)
-
-    def to_native(self, pk):
-        return pk
-
-    def field_to_native(self, obj, field_name):
-        try:
-            # Prefer obj.serializable_value for performance reasons
-            queryset = obj.serializable_value(self.source or field_name)
-        except AttributeError:
-            # RelatedManager (reverse relationship)
-            queryset = getattr(obj, self.source or field_name)
-            return [self.to_native(item.pk) for item in queryset.all()]
-        # Forward relationship
-        return [self.to_native(item.pk) for item in queryset.all()]
-
-    def from_native(self, data):
-        if self.queryset is None:
-            raise Exception('Writable related fields must include a `queryset` argument')
-
-        try:
-            return self.queryset.get(pk=data)
-        except ObjectDoesNotExist:
-            msg = "Invalid pk '%s' - object does not exist." % smart_unicode(data)
-            raise ValidationError(msg)
-
-### Slug relationships
-
-
-class SlugRelatedField(RelatedField):
-    default_read_only = False
-    form_field_class = forms.ChoiceField
-
-    def __init__(self, *args, **kwargs):
-        self.slug_field = kwargs.pop('slug_field', None)
-        assert self.slug_field, 'slug_field is required'
-        super(SlugRelatedField, self).__init__(*args, **kwargs)
-
-    def to_native(self, obj):
-        return getattr(obj, self.slug_field)
-
-    def from_native(self, data):
-        if self.queryset is None:
-            raise Exception('Writable related fields must include a `queryset` argument')
-
-        try:
-            return self.queryset.get(**{self.slug_field: data})
-        except ObjectDoesNotExist:
-            raise ValidationError('Object with %s=%s does not exist.' %
-                                  (self.slug_field, unicode(data)))
-
-
-class ManySlugRelatedField(ManyRelatedMixin, SlugRelatedField):
-    form_field_class = forms.MultipleChoiceField
-
-
-### Hyperlinked relationships
-
-class HyperlinkedRelatedField(RelatedField):
-    """
-    Represents a to-one relationship, using hyperlinking.
-    """
-    pk_url_kwarg = 'pk'
-    slug_field = 'slug'
-    slug_url_kwarg = None  # Defaults to same as `slug_field` unless overridden
-    default_read_only = False
-    form_field_class = forms.ChoiceField
-
-    def __init__(self, *args, **kwargs):
-        try:
-            self.view_name = kwargs.pop('view_name')
-        except:
-            raise ValueError("Hyperlinked field requires 'view_name' 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):
-        """
-        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)
-        pk = getattr(obj, 'pk', None)
-        if pk is None:
-            return
-        kwargs = {self.pk_url_kwarg: pk}
-        try:
-            return reverse(view_name, kwargs=kwargs, request=request, format=format)
-        except:
-            pass
-
-        slug = getattr(obj, self.slug_field, None)
-
-        if not slug:
-            raise ValidationError('Could not resolve URL for field using view name "%s"' % view_name)
-
-        kwargs = {self.slug_url_kwarg: slug}
-        try:
-            return reverse(self.view_name, kwargs=kwargs, request=request, format=format)
-        except:
-            pass
-
-        kwargs = {self.pk_url_kwarg: obj.pk, self.slug_url_kwarg: slug}
-        try:
-            return reverse(self.view_name, kwargs=kwargs, request=request, format=format)
-        except:
-            pass
-
-        raise ValidationError('Could not resolve URL for field using view name "%s"' % view_name)
-
-    def from_native(self, value):
-        # Convert URL -> model instance pk
-        # TODO: Use values_list
-        if self.queryset is None:
-            raise Exception('Writable related fields must include a `queryset` argument')
-
-        if value.startswith('http:') or value.startswith('https:'):
-            # If needed convert absolute URLs to relative path
-            value = urlparse(value).path
-            prefix = get_script_prefix()
-            if value.startswith(prefix):
-                value = '/' + value[len(prefix):]
-
-        try:
-            match = resolve(value)
-        except:
-            raise ValidationError('Invalid hyperlink - No URL match')
-
-        if match.url_name != self.view_name:
-            raise ValidationError('Invalid hyperlink - Incorrect URL 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 an error.
-        else:
-            raise ValidationError('Invalid hyperlink')
-
-        try:
-            obj = queryset.get()
-        except ObjectDoesNotExist:
-            raise ValidationError('Invalid hyperlink - object does not exist.')
-        return obj
-
-
-class ManyHyperlinkedRelatedField(ManyRelatedMixin, HyperlinkedRelatedField):
-    """
-    Represents a to-many relationship, using hyperlinking.
-    """
-    form_field_class = forms.MultipleChoiceField
-
-
-class HyperlinkedIdentityField(Field):
-    """
-    Represents the instance, or a property on the instance, using hyperlinking.
-    """
-    pk_url_kwarg = 'pk'
-    slug_field = 'slug'
-    slug_url_kwarg = None  # Defaults to same as `slug_field` unless overridden
-
-    def __init__(self, *args, **kwargs):
-        # TODO: Make view_name mandatory, and have the
-        # HyperlinkedModelSerializer set it on-the-fly
-        self.view_name = kwargs.pop('view_name', None)
-        self.format = kwargs.pop('format', None)
-
-        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)
-
-        super(HyperlinkedIdentityField, self).__init__(*args, **kwargs)
-
-    def field_to_native(self, obj, field_name):
-        request = self.context.get('request', None)
-        format = self.format or self.context.get('format', None)
-        view_name = self.view_name or self.parent.opts.view_name
-        kwargs = {self.pk_url_kwarg: obj.pk}
-        try:
-            return reverse(view_name, kwargs=kwargs, request=request, format=format)
-        except:
-            pass
-
-        slug = getattr(obj, self.slug_field, None)
-
-        if not slug:
-            raise ValidationError('Could not resolve URL for field using view name "%s"' % view_name)
-
-        kwargs = {self.slug_url_kwarg: slug}
-        try:
-            return reverse(self.view_name, kwargs=kwargs, request=request, format=format)
-        except:
-            pass
-
-        kwargs = {self.pk_url_kwarg: obj.pk, self.slug_url_kwarg: slug}
-        try:
-            return reverse(self.view_name, kwargs=kwargs, request=request, format=format)
-        except:
-            pass
-
-        raise ValidationError('Could not resolve URL for field using view name "%s"' % view_name)
-
 
 ##### Typed Fields #####
 
diff --git a/rest_framework/relations.py b/rest_framework/relations.py
new file mode 100644
index 00000000..9b3a7790
--- /dev/null
+++ b/rest_framework/relations.py
@@ -0,0 +1,446 @@
+from django.core.exceptions import ObjectDoesNotExist, ValidationError
+from django.core.urlresolvers import resolve, get_script_prefix
+from django import forms
+from django.forms import widgets
+from django.forms.models import ModelChoiceIterator
+from django.utils.encoding import smart_unicode
+from rest_framework.fields import Field, WritableField
+from rest_framework.reverse import reverse
+from urlparse import urlparse
+
+##### Relational fields #####
+
+
+# Not actually Writable, but subclasses may need to be.
+class RelatedField(WritableField):
+    """
+    Base class for related model fields.
+
+    If not overridden, this represents a to-one relationship, using the unicode
+    representation of the target.
+    """
+    widget = widgets.Select
+    cache_choices = False
+    empty_label = None
+    default_read_only = True  # TODO: Remove this
+
+    def __init__(self, *args, **kwargs):
+        self.queryset = kwargs.pop('queryset', None)
+        self.null = kwargs.pop('null', False)
+        super(RelatedField, self).__init__(*args, **kwargs)
+        self.read_only = kwargs.pop('read_only', self.default_read_only)
+
+    def initialize(self, parent, field_name):
+        super(RelatedField, self).initialize(parent, field_name)
+        if self.queryset is None and not self.read_only:
+            try:
+                manager = getattr(self.parent.opts.model, self.source or field_name)
+                if hasattr(manager, 'related'):  # Forward
+                    self.queryset = manager.related.model._default_manager.all()
+                else:  # Reverse
+                    self.queryset = manager.field.rel.to._default_manager.all()
+            except:
+                raise
+                msg = ('Serializer related fields must include a `queryset`' +
+                       ' argument or set `read_only=True')
+                raise Exception(msg)
+
+    ### We need this stuff to make form choices work...
+
+    # def __deepcopy__(self, memo):
+    #     result = super(RelatedField, self).__deepcopy__(memo)
+    #     result.queryset = result.queryset
+    #     return result
+
+    def prepare_value(self, obj):
+        return self.to_native(obj)
+
+    def label_from_instance(self, obj):
+        """
+        Return a readable representation for use with eg. select widgets.
+        """
+        desc = smart_unicode(obj)
+        ident = smart_unicode(self.to_native(obj))
+        if desc == ident:
+            return desc
+        return "%s - %s" % (desc, ident)
+
+    def _get_queryset(self):
+        return self._queryset
+
+    def _set_queryset(self, queryset):
+        self._queryset = queryset
+        self.widget.choices = self.choices
+
+    queryset = property(_get_queryset, _set_queryset)
+
+    def _get_choices(self):
+        # If self._choices is set, then somebody must have manually set
+        # the property self.choices. In this case, just return self._choices.
+        if hasattr(self, '_choices'):
+            return self._choices
+
+        # Otherwise, execute the QuerySet in self.queryset to determine the
+        # choices dynamically. Return a fresh ModelChoiceIterator that has not been
+        # consumed. Note that we're instantiating a new ModelChoiceIterator *each*
+        # time _get_choices() is called (and, thus, each time self.choices is
+        # accessed) so that we can ensure the QuerySet has not been consumed. This
+        # construct might look complicated but it allows for lazy evaluation of
+        # the queryset.
+        return ModelChoiceIterator(self)
+
+    def _set_choices(self, value):
+        # Setting choices also sets the choices on the widget.
+        # choices can be any iterable, but we call list() on it because
+        # it will be consumed more than once.
+        self._choices = self.widget.choices = list(value)
+
+    choices = property(_get_choices, _set_choices)
+
+    ### Regular serializer stuff...
+
+    def field_to_native(self, obj, field_name):
+        value = getattr(obj, self.source or field_name)
+        return self.to_native(value)
+
+    def field_from_native(self, data, files, field_name, into):
+        if self.read_only:
+            return
+
+        try:
+            value = data[field_name]
+        except KeyError:
+            if self.required:
+                raise ValidationError(self.error_messages['required'])
+            return
+
+        if value in (None, '') and not self.null:
+            raise ValidationError('Value may not be null')
+        elif value in (None, '') and self.null:
+            into[(self.source or field_name)] = None
+        else:
+            into[(self.source or field_name)] = self.from_native(value)
+
+
+class ManyRelatedMixin(object):
+    """
+    Mixin to convert a related field to a many related field.
+    """
+    widget = widgets.SelectMultiple
+
+    def field_to_native(self, obj, field_name):
+        value = getattr(obj, self.source or field_name)
+        return [self.to_native(item) for item in value.all()]
+
+    def field_from_native(self, data, files, field_name, into):
+        if self.read_only:
+            return
+
+        try:
+            # Form data
+            value = data.getlist(self.source or field_name)
+        except:
+            # Non-form data
+            value = data.get(self.source or field_name)
+        else:
+            if value == ['']:
+                value = []
+
+        into[field_name] = [self.from_native(item) for item in value]
+
+
+class ManyRelatedField(ManyRelatedMixin, RelatedField):
+    """
+    Base class for related model managers.
+
+    If not overridden, this represents a to-many relationship, using the unicode
+    representations of the target, and is read-only.
+    """
+    pass
+
+
+### PrimaryKey relationships
+
+class PrimaryKeyRelatedField(RelatedField):
+    """
+    Represents a to-one relationship as a pk value.
+    """
+    default_read_only = False
+    form_field_class = forms.ChoiceField
+
+    # TODO: Remove these field hacks...
+    def prepare_value(self, obj):
+        return self.to_native(obj.pk)
+
+    def label_from_instance(self, obj):
+        """
+        Return a readable representation for use with eg. select widgets.
+        """
+        desc = smart_unicode(obj)
+        ident = smart_unicode(self.to_native(obj.pk))
+        if desc == ident:
+            return desc
+        return "%s - %s" % (desc, ident)
+
+    # TODO: Possibly change this to just take `obj`, through prob less performant
+    def to_native(self, pk):
+        return pk
+
+    def from_native(self, data):
+        if self.queryset is None:
+            raise Exception('Writable related fields must include a `queryset` argument')
+
+        try:
+            return self.queryset.get(pk=data)
+        except ObjectDoesNotExist:
+            msg = "Invalid pk '%s' - object does not exist." % smart_unicode(data)
+            raise ValidationError(msg)
+
+    def field_to_native(self, obj, field_name):
+        try:
+            # Prefer obj.serializable_value for performance reasons
+            pk = obj.serializable_value(self.source or field_name)
+        except AttributeError:
+            # RelatedObject (reverse relationship)
+            obj = getattr(obj, self.source or field_name)
+            return self.to_native(obj.pk)
+        # Forward relationship
+        return self.to_native(pk)
+
+
+class ManyPrimaryKeyRelatedField(ManyRelatedField):
+    """
+    Represents a to-many relationship as a pk value.
+    """
+    default_read_only = False
+    form_field_class = forms.MultipleChoiceField
+
+    def prepare_value(self, obj):
+        return self.to_native(obj.pk)
+
+    def label_from_instance(self, obj):
+        """
+        Return a readable representation for use with eg. select widgets.
+        """
+        desc = smart_unicode(obj)
+        ident = smart_unicode(self.to_native(obj.pk))
+        if desc == ident:
+            return desc
+        return "%s - %s" % (desc, ident)
+
+    def to_native(self, pk):
+        return pk
+
+    def field_to_native(self, obj, field_name):
+        try:
+            # Prefer obj.serializable_value for performance reasons
+            queryset = obj.serializable_value(self.source or field_name)
+        except AttributeError:
+            # RelatedManager (reverse relationship)
+            queryset = getattr(obj, self.source or field_name)
+            return [self.to_native(item.pk) for item in queryset.all()]
+        # Forward relationship
+        return [self.to_native(item.pk) for item in queryset.all()]
+
+    def from_native(self, data):
+        if self.queryset is None:
+            raise Exception('Writable related fields must include a `queryset` argument')
+
+        try:
+            return self.queryset.get(pk=data)
+        except ObjectDoesNotExist:
+            msg = "Invalid pk '%s' - object does not exist." % smart_unicode(data)
+            raise ValidationError(msg)
+
+### Slug relationships
+
+
+class SlugRelatedField(RelatedField):
+    default_read_only = False
+    form_field_class = forms.ChoiceField
+
+    def __init__(self, *args, **kwargs):
+        self.slug_field = kwargs.pop('slug_field', None)
+        assert self.slug_field, 'slug_field is required'
+        super(SlugRelatedField, self).__init__(*args, **kwargs)
+
+    def to_native(self, obj):
+        return getattr(obj, self.slug_field)
+
+    def from_native(self, data):
+        if self.queryset is None:
+            raise Exception('Writable related fields must include a `queryset` argument')
+
+        try:
+            return self.queryset.get(**{self.slug_field: data})
+        except ObjectDoesNotExist:
+            raise ValidationError('Object with %s=%s does not exist.' %
+                                  (self.slug_field, unicode(data)))
+
+
+class ManySlugRelatedField(ManyRelatedMixin, SlugRelatedField):
+    form_field_class = forms.MultipleChoiceField
+
+
+### Hyperlinked relationships
+
+class HyperlinkedRelatedField(RelatedField):
+    """
+    Represents a to-one relationship, using hyperlinking.
+    """
+    pk_url_kwarg = 'pk'
+    slug_field = 'slug'
+    slug_url_kwarg = None  # Defaults to same as `slug_field` unless overridden
+    default_read_only = False
+    form_field_class = forms.ChoiceField
+
+    def __init__(self, *args, **kwargs):
+        try:
+            self.view_name = kwargs.pop('view_name')
+        except:
+            raise ValueError("Hyperlinked field requires 'view_name' 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):
+        """
+        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)
+        pk = getattr(obj, 'pk', None)
+        if pk is None:
+            return
+        kwargs = {self.pk_url_kwarg: pk}
+        try:
+            return reverse(view_name, kwargs=kwargs, request=request, format=format)
+        except:
+            pass
+
+        slug = getattr(obj, self.slug_field, None)
+
+        if not slug:
+            raise ValidationError('Could not resolve URL for field using view name "%s"' % view_name)
+
+        kwargs = {self.slug_url_kwarg: slug}
+        try:
+            return reverse(self.view_name, kwargs=kwargs, request=request, format=format)
+        except:
+            pass
+
+        kwargs = {self.pk_url_kwarg: obj.pk, self.slug_url_kwarg: slug}
+        try:
+            return reverse(self.view_name, kwargs=kwargs, request=request, format=format)
+        except:
+            pass
+
+        raise ValidationError('Could not resolve URL for field using view name "%s"' % view_name)
+
+    def from_native(self, value):
+        # Convert URL -> model instance pk
+        # TODO: Use values_list
+        if self.queryset is None:
+            raise Exception('Writable related fields must include a `queryset` argument')
+
+        if value.startswith('http:') or value.startswith('https:'):
+            # If needed convert absolute URLs to relative path
+            value = urlparse(value).path
+            prefix = get_script_prefix()
+            if value.startswith(prefix):
+                value = '/' + value[len(prefix):]
+
+        try:
+            match = resolve(value)
+        except:
+            raise ValidationError('Invalid hyperlink - No URL match')
+
+        if match.url_name != self.view_name:
+            raise ValidationError('Invalid hyperlink - Incorrect URL 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 an error.
+        else:
+            raise ValidationError('Invalid hyperlink')
+
+        try:
+            obj = queryset.get()
+        except ObjectDoesNotExist:
+            raise ValidationError('Invalid hyperlink - object does not exist.')
+        return obj
+
+
+class ManyHyperlinkedRelatedField(ManyRelatedMixin, HyperlinkedRelatedField):
+    """
+    Represents a to-many relationship, using hyperlinking.
+    """
+    form_field_class = forms.MultipleChoiceField
+
+
+class HyperlinkedIdentityField(Field):
+    """
+    Represents the instance, or a property on the instance, using hyperlinking.
+    """
+    pk_url_kwarg = 'pk'
+    slug_field = 'slug'
+    slug_url_kwarg = None  # Defaults to same as `slug_field` unless overridden
+
+    def __init__(self, *args, **kwargs):
+        # TODO: Make view_name mandatory, and have the
+        # HyperlinkedModelSerializer set it on-the-fly
+        self.view_name = kwargs.pop('view_name', None)
+        self.format = kwargs.pop('format', None)
+
+        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)
+
+        super(HyperlinkedIdentityField, self).__init__(*args, **kwargs)
+
+    def field_to_native(self, obj, field_name):
+        request = self.context.get('request', None)
+        format = self.format or self.context.get('format', None)
+        view_name = self.view_name or self.parent.opts.view_name
+        kwargs = {self.pk_url_kwarg: obj.pk}
+        try:
+            return reverse(view_name, kwargs=kwargs, request=request, format=format)
+        except:
+            pass
+
+        slug = getattr(obj, self.slug_field, None)
+
+        if not slug:
+            raise ValidationError('Could not resolve URL for field using view name "%s"' % view_name)
+
+        kwargs = {self.slug_url_kwarg: slug}
+        try:
+            return reverse(self.view_name, kwargs=kwargs, request=request, format=format)
+        except:
+            pass
+
+        kwargs = {self.pk_url_kwarg: obj.pk, self.slug_url_kwarg: slug}
+        try:
+            return reverse(self.view_name, kwargs=kwargs, request=request, format=format)
+        except:
+            pass
+
+        raise ValidationError('Could not resolve URL for field using view name "%s"' % view_name)
diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index e8e6735a..ed173d85 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -14,7 +14,7 @@ from rest_framework.compat import get_concrete_model
 # This helps keep the seperation between model fields, form fields, and
 # serializer fields more explicit.
 
-
+from rest_framework.relations import *
 from rest_framework.fields import *