Remove a few no longer needed compat checks and references (#7092)

* serializers: removes no longer needed compat checks

UUIDField and DurationField are both supported in all supported Django
versions.

IPAddressField was removed in Django 1.9, which is no longer supported.

* serializers: move related code closer together

This way it's easier to see all of the mappings in one place.

* serializers,docs: remove some DRF 2.x references

The last release of DRF 2.x was 5 years ago, it seems fine to remove
these references now.

docs/api-guide/fields.md

@@ -597,8 +597,6 @@ The `.to_representation()` method is called to convert the initial datatype into
 
 The `to_internal_value()` method is called to restore a primitive datatype into its internal python representation. This method should raise a `serializers.ValidationError` if the data is invalid.
 
-Note that the `WritableField` class that was present in version 2.x no longer exists. You should subclass `Field` and override `to_internal_value()` if the field supports data input.
-
 ## Examples
 
 ### A Basic Custom Field

docs/api-guide/generic-views.md

@@ -175,8 +175,6 @@ You can also use these hooks to provide additional validation, by raising a `Val
             raise ValidationError('You have already signed up')
         serializer.save(user=self.request.user)
 
-**Note**: These methods replace the old-style version 2.x `pre_save`, `post_save`, `pre_delete` and `post_delete` methods, which are no longer available.
-
 **Other methods**:
 
 You won't typically need to override the following methods, although you might need to call into them if you're writing custom views using `GenericAPIView`.

rest_framework/serializers.py

@@ -19,7 +19,6 @@ from collections.abc import Mapping
 from django.core.exceptions import FieldDoesNotExist, ImproperlyConfigured
 from django.core.exceptions import ValidationError as DjangoValidationError
 from django.db import models
-from django.db.models import DurationField as ModelDurationField
 from django.db.models.fields import Field as DjangoModelField
 from django.utils import timezone
 from django.utils.functional import cached_property
@@ -167,13 +166,6 @@ class BaseSerializer(Field):
         raise NotImplementedError('`create()` must be implemented.')
 
     def save(self, **kwargs):
-        assert not hasattr(self, 'save_object'), (
-            'Serializer `%s.%s` has old-style version 2 `.save_object()` '
-            'that is no longer compatible with REST framework 3. '
-            'Use the new-style `.create()` and `.update()` methods instead.' %
-            (self.__class__.__module__, self.__class__.__name__)
-        )
-
         assert hasattr(self, '_errors'), (
             'You must call `.is_valid()` before calling `.save()`.'
         )
@@ -217,13 +209,6 @@ class BaseSerializer(Field):
         return self.instance
 
     def is_valid(self, raise_exception=False):
-        assert not hasattr(self, 'restore_object'), (
-            'Serializer `%s.%s` has old-style version 2 `.restore_object()` '
-            'that is no longer compatible with REST framework 3. '
-            'Use the new-style `.create()` and `.update()` methods instead.' %
-            (self.__class__.__module__, self.__class__.__name__)
-        )
-
         assert hasattr(self, 'initial_data'), (
             'Cannot call `.is_valid()` as no `data=` keyword argument was '
             'passed when instantiating the serializer instance.'
@@ -876,6 +861,7 @@ class ModelSerializer(Serializer):
         models.DateField: DateField,
         models.DateTimeField: DateTimeField,
         models.DecimalField: DecimalField,
+        models.DurationField: DurationField,
         models.EmailField: EmailField,
         models.Field: ModelField,
         models.FileField: FileField,
@@ -890,11 +876,14 @@ class ModelSerializer(Serializer):
         models.TextField: CharField,
         models.TimeField: TimeField,
         models.URLField: URLField,
+        models.UUIDField: UUIDField,
         models.GenericIPAddressField: IPAddressField,
         models.FilePathField: FilePathField,
     }
-    if ModelDurationField is not None:
+    if postgres_fields:
-        serializer_field_mapping[ModelDurationField] = DurationField
+        serializer_field_mapping[postgres_fields.HStoreField] = HStoreField
+        serializer_field_mapping[postgres_fields.ArrayField] = ListField
+        serializer_field_mapping[postgres_fields.JSONField] = JSONField
     serializer_related_field = PrimaryKeyRelatedField
     serializer_related_to_field = SlugRelatedField
     serializer_url_field = HyperlinkedIdentityField
@@ -1585,19 +1574,6 @@ class ModelSerializer(Serializer):
         return validators
 
 
-if hasattr(models, 'UUIDField'):
-    ModelSerializer.serializer_field_mapping[models.UUIDField] = UUIDField
-
-# IPAddressField is deprecated in Django
-if hasattr(models, 'IPAddressField'):
-    ModelSerializer.serializer_field_mapping[models.IPAddressField] = IPAddressField
-
-if postgres_fields:
-    ModelSerializer.serializer_field_mapping[postgres_fields.HStoreField] = HStoreField
-    ModelSerializer.serializer_field_mapping[postgres_fields.ArrayField] = ListField
-    ModelSerializer.serializer_field_mapping[postgres_fields.JSONField] = JSONField
-
-
 class HyperlinkedModelSerializer(ModelSerializer):
     """
     A type of `ModelSerializer` that uses hyperlinked relationships instead