Merge NullBooleanField with BooleanField(allow_null=True) (#7122)

* Make `NullBooleanField` subclass `BooleanField`

This removes a lot of the redundancy that was in place becuase we
were not doing this. This maintains the `None` initial value that
was previously present, as well as disallowing `allow_null` to be
passed in.

* Remove special case for mapping `NullBooleanField`

In newer versions of Django, the `NullBooleanField` is handled the
same way as a `BooleanField(null=True)`. Given that we also support
that combination, and that our own `NullBooleanField` behaves in the
same manner, it makes sense to remove the special casing that exists
for it.

* Add test for BooleanField(null=True, choices)

* Remove special case for NullBooleanField

* Adjust mapping tests for NullBooleanField

* Fixed linting error

* Raise deprecation warning when NullBooleanField is used

* Fix linting issue in imports

rest_framework/__init__.py

@@ -31,3 +31,7 @@ class RemovedInDRF313Warning(DeprecationWarning):
 
 class RemovedInDRF314Warning(PendingDeprecationWarning):
     pass
+
+
+class RemovedInDRF314Warning(PendingDeprecationWarning):
+    pass

rest_framework/fields.py

@@ -30,7 +30,9 @@ from django.utils.timezone import utc
 from django.utils.translation import gettext_lazy as _
 from pytz.exceptions import InvalidTimeError
 
-from rest_framework import ISO_8601, RemovedInDRF313Warning
+from rest_framework import (
+    ISO_8601, RemovedInDRF313Warning, RemovedInDRF314Warning
+)
 from rest_framework.compat import ProhibitNullCharactersValidator
 from rest_framework.exceptions import ErrorDetail, ValidationError
 from rest_framework.settings import api_settings
@@ -740,55 +742,22 @@ class BooleanField(Field):
         return bool(value)
 
 
-class NullBooleanField(Field):
-    default_error_messages = {
-        'invalid': _('Must be a valid boolean.')
-    }
+class NullBooleanField(BooleanField):
     initial = None
-    TRUE_VALUES = {
-        't', 'T',
-        'y', 'Y', 'yes', 'YES',
-        'true', 'True', 'TRUE',
-        'on', 'On', 'ON',
-        '1', 1,
-        True
-    }
-    FALSE_VALUES = {
-        'f', 'F',
-        'n', 'N', 'no', 'NO',
-        'false', 'False', 'FALSE',
-        'off', 'Off', 'OFF',
-        '0', 0, 0.0,
-        False
-    }
-    NULL_VALUES = {'null', 'Null', 'NULL', '', None}
 
     def __init__(self, **kwargs):
+        warnings.warn(
+            "The `NullBooleanField` is deprecated and will be removed starting "
+            "with 3.14. Instead use the `BooleanField` field and set "
+            "`null=True` which does the same thing.",
+            RemovedInDRF314Warning, stacklevel=2
+        )
+
         assert 'allow_null' not in kwargs, '`allow_null` is not a valid option.'
         kwargs['allow_null'] = True
+
         super().__init__(**kwargs)
 
-    def to_internal_value(self, data):
-        try:
-            if data in self.TRUE_VALUES:
-                return True
-            elif data in self.FALSE_VALUES:
-                return False
-            elif data in self.NULL_VALUES:
-                return None
-        except TypeError:  # Input is an unhashable type
-            pass
-        self.fail('invalid', input=data)
-
-    def to_representation(self, value):
-        if value in self.NULL_VALUES:
-            return None
-        if value in self.TRUE_VALUES:
-            return True
-        elif value in self.FALSE_VALUES:
-            return False
-        return bool(value)
-
 
 # String types...
 

rest_framework/serializers.py

@@ -868,7 +868,7 @@ class ModelSerializer(Serializer):
         models.FloatField: FloatField,
         models.ImageField: ImageField,
         models.IntegerField: IntegerField,
-        models.NullBooleanField: NullBooleanField,
+        models.NullBooleanField: BooleanField,
         models.PositiveIntegerField: IntegerField,
         models.PositiveSmallIntegerField: IntegerField,
         models.SlugField: SlugField,

rest_framework/utils/field_mapping.py

@@ -104,7 +104,7 @@ def get_field_kwargs(field_name, model_field):
     if model_field.has_default() or model_field.blank or model_field.null:
         kwargs['required'] = False
 
-    if model_field.null and not isinstance(model_field, models.NullBooleanField):
+    if model_field.null:
         kwargs['allow_null'] = True
 
     if model_field.blank and (isinstance(model_field, (models.CharField, models.TextField))):

tests/test_model_serializer.py

@@ -182,7 +182,7 @@ class TestRegularFieldMappings(TestCase):
                 email_field = EmailField(max_length=100)
                 float_field = FloatField()
                 integer_field = IntegerField()
-                null_boolean_field = NullBooleanField(required=False)
+                null_boolean_field = BooleanField(allow_null=True, required=False)
                 positive_integer_field = IntegerField()
                 positive_small_integer_field = IntegerField()
                 slug_field = SlugField(allow_unicode=False, max_length=100)
@@ -236,6 +236,27 @@ class TestRegularFieldMappings(TestCase):
 
         self.assertEqual(repr(NullableBooleanSerializer()), expected)
 
+    def test_nullable_boolean_field_choices(self):
+        class NullableBooleanChoicesModel(models.Model):
+            CHECKLIST_OPTIONS = (
+                (None, 'Unknown'),
+                (True, 'Yes'),
+                (False, 'No'),
+            )
+
+            field = models.BooleanField(null=True, choices=CHECKLIST_OPTIONS)
+
+        class NullableBooleanChoicesSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = NullableBooleanChoicesModel
+                fields = ['field']
+
+        serializer = NullableBooleanChoicesSerializer(data=dict(
+            field=None,
+        ))
+        self.assertTrue(serializer.is_valid())
+        self.assertEqual(serializer.errors, {})
+
     def test_method_field(self):
         """
         Properties and methods on the model should be allowed as `Meta.fields`