Make model fields with a db_default optional in ModelSerializer

docs/api-guide/fields.md

@@ -39,7 +39,7 @@ Set to false if this field is not required to be present during deserialization.
 
 Setting this to `False` also allows the object attribute or dictionary key to be omitted from output when serializing the instance. If the key is not present it will simply not be included in the output representation.
 
-Defaults to `True`. If you're using [Model Serializer](https://www.django-rest-framework.org/api-guide/serializers/#modelserializer), the default value will be `False` when you have specified a `default`, or when the corresponding `Model` field has `blank=True` or `null=True` and is not part of a unique constraint at the same time. (Note that without a `default` value, [unique constraints will cause the field to be required](https://www.django-rest-framework.org/api-guide/validators/#optional-fields).)
+Defaults to `True`. If you're using [Model Serializer](https://www.django-rest-framework.org/api-guide/serializers/#modelserializer), the default value will be `False` when you have specified a `default`, or when the corresponding `Model` field has a `db_default`, `blank=True` or `null=True` and is not part of a unique constraint at the same time. (Note that without a `default` value, [unique constraints will cause the field to be required](https://www.django-rest-framework.org/api-guide/validators/#optional-fields).)
 
 ### `default`
 

rest_framework/utils/field_mapping.py

@@ -138,7 +138,7 @@ def get_field_kwargs(field_name, model_field):
         kwargs['read_only'] = True
         return kwargs
 
-    if model_field.has_default() or model_field.blank or model_field.null:
+    if model_field.has_default() or model_field.has_db_default() or model_field.blank or model_field.null:
         kwargs['required'] = False
 
     if model_field.blank and (isinstance(model_field, (models.CharField, models.TextField))):
@@ -304,7 +304,7 @@ def get_relation_kwargs(field_name, relation_info):
             # No further keyword arguments are valid.
             return kwargs
 
-        if model_field.has_default() or model_field.blank or model_field.null:
+        if model_field.has_default() or model_field.has_db_default() or model_field.blank or model_field.null:
             kwargs['required'] = False
         if model_field.validators:
             kwargs['validators'] = model_field.validators

tests/test_model_serializer.py

@@ -20,6 +20,7 @@
     MinValueValidator
 )
 from django.db import models
+from django.db.models.functions import Now
 from django.db.models.signals import m2m_changed
 from django.dispatch import receiver
 from django.test import TestCase
@@ -381,6 +382,24 @@ class Meta:
         assert non_editable_choice_field.read_only is True
         assert non_editable_choice_field.choices
 
+    def test_db_default_field_not_required(self):
+        class DBDefaultModel(models.Model):
+            db_default_field = models.IntegerField(db_default=0)
+            db_default_expression_field = models.DateTimeField(db_default=Now())
+
+        class TestSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = DBDefaultModel
+                fields = '__all__'
+
+        expected = dedent(r"""
+            TestSerializer\(\):
+                id = IntegerField\(label='ID', read_only=True\)
+                db_default_field = IntegerField\(.*required=False\)
+                db_default_expression_field = DateTimeField\(required=False\)
+        """)
+        assert re.search(expected, repr(TestSerializer())) is not None
+
 
 class TestDurationFieldMapping(TestCase):
     def test_duration_field(self):
@@ -656,6 +675,22 @@ class Meta:
         """)
         self.assertEqual(repr(TestSerializer()), expected)
 
+    def test_foreign_key_with_db_default(self):
+        class DBDefaultForeignKeyModel(models.Model):
+            foreign_key = models.ForeignKey(ForeignKeyTargetModel, on_delete=models.CASCADE, db_default=1)
+
+        class TestSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = DBDefaultForeignKeyModel
+                fields = '__all__'
+
+        expected = dedent("""
+            TestSerializer():
+                id = IntegerField(label='ID', read_only=True)
+                foreign_key = PrimaryKeyRelatedField(queryset=ForeignKeyTargetModel.objects.all(), required=False)
+        """)
+        self.assertEqual(repr(TestSerializer()), expected)
+
     def test_nested_relations(self):
         class TestSerializer(serializers.ModelSerializer):
             class Meta: