Made it easier to change the field name of ModelSerializer.

Added a way to override the ManyRelatedField class to use by an RelatedField

The ManyRelatedField class was not changed by this commit, it had to be moved
before the RelatedField class.

See #3121

rest_framework/relations.py

@@ -35,7 +35,67 @@ MANY_RELATION_KWARGS = (
 )
 
 
+class ManyRelatedField(Field):
+    """
+    Relationships with `many=True` transparently get coerced into instead being
+    a ManyRelatedField with a child relationship.
+
+    The `ManyRelatedField` class is responsible for handling iterating through
+    the values and passing each one to the child relationship.
+
+    This class is treated as private API.
+    You shouldn't generally need to be using this class directly yourself,
+    and should instead simply set 'many=True' on the relationship.
+    """
+    initial = []
+    default_empty_html = []
+
+    def __init__(self, child_relation=None, *args, **kwargs):
+        self.child_relation = child_relation
+        assert child_relation is not None, '`child_relation` is a required argument.'
+        super(ManyRelatedField, self).__init__(*args, **kwargs)
+        self.child_relation.bind(field_name='', parent=self)
+
+    def get_value(self, dictionary):
+        # We override the default field access in order to support
+        # lists in HTML forms.
+        if html.is_html_input(dictionary):
+            # Don't return [] if the update is partial
+            if self.field_name not in dictionary:
+                if getattr(self.root, 'partial', False):
+                    return empty
+            return dictionary.getlist(self.field_name)
+
+        return dictionary.get(self.field_name, empty)
+
+    def to_internal_value(self, data):
+        return [
+            self.child_relation.to_internal_value(item)
+            for item in data
+        ]
+
+    def get_attribute(self, instance):
+        # Can't have any relationships if not created
+        if hasattr(instance, 'pk') and instance.pk is None:
+            return []
+
+        relationship = get_attribute(instance, self.source_attrs)
+        return relationship.all() if (hasattr(relationship, 'all')) else relationship
+
+    def to_representation(self, iterable):
+        return [
+            self.child_relation.to_representation(value)
+            for value in iterable
+        ]
+
+    @property
+    def choices(self):
+        return self.child_relation.choices
+
+
 class RelatedField(Field):
+    many_related_field_class = ManyRelatedField
+
     def __init__(self, **kwargs):
         self.queryset = kwargs.pop('queryset', None)
         assert self.queryset is not None or kwargs.get('read_only', None), (
@@ -77,7 +137,7 @@ class RelatedField(Field):
         for key in kwargs.keys():
             if key in MANY_RELATION_KWARGS:
                 list_kwargs[key] = kwargs[key]
-        return ManyRelatedField(**list_kwargs)
+        return cls.many_related_field_class(**list_kwargs)
 
     def run_validation(self, data=empty):
         # We force empty strings to None values for relational fields.
@@ -338,61 +398,3 @@ class SlugRelatedField(RelatedField):
 
     def to_representation(self, obj):
         return getattr(obj, self.slug_field)
-
-
-class ManyRelatedField(Field):
-    """
-    Relationships with `many=True` transparently get coerced into instead being
-    a ManyRelatedField with a child relationship.
-
-    The `ManyRelatedField` class is responsible for handling iterating through
-    the values and passing each one to the child relationship.
-
-    This class is treated as private API.
-    You shouldn't generally need to be using this class directly yourself,
-    and should instead simply set 'many=True' on the relationship.
-    """
-    initial = []
-    default_empty_html = []
-
-    def __init__(self, child_relation=None, *args, **kwargs):
-        self.child_relation = child_relation
-        assert child_relation is not None, '`child_relation` is a required argument.'
-        super(ManyRelatedField, self).__init__(*args, **kwargs)
-        self.child_relation.bind(field_name='', parent=self)
-
-    def get_value(self, dictionary):
-        # We override the default field access in order to support
-        # lists in HTML forms.
-        if html.is_html_input(dictionary):
-            # Don't return [] if the update is partial
-            if self.field_name not in dictionary:
-                if getattr(self.root, 'partial', False):
-                    return empty
-            return dictionary.getlist(self.field_name)
-
-        return dictionary.get(self.field_name, empty)
-
-    def to_internal_value(self, data):
-        return [
-            self.child_relation.to_internal_value(item)
-            for item in data
-        ]
-
-    def get_attribute(self, instance):
-        # Can't have any relationships if not created
-        if hasattr(instance, 'pk') and instance.pk is None:
-            return []
-
-        relationship = get_attribute(instance, self.source_attrs)
-        return relationship.all() if (hasattr(relationship, 'all')) else relationship
-
-    def to_representation(self, iterable):
-        return [
-            self.child_relation.to_representation(value)
-            for value in iterable
-        ]
-
-    @property
-    def choices(self):
-        return self.child_relation.choices