Add better approach

Author: mgaligniana

rest_framework/renderers.py

@@ -22,7 +22,7 @@
 from django.utils.http import parse_header_parameters
 from django.utils.safestring import SafeString
 
-from rest_framework import VERSION, exceptions, serializers, status
+from rest_framework import ISO_8601, VERSION, exceptions, serializers, status
 from rest_framework.compat import (
     INDENT_SEPARATORS, LONG_SEPARATORS, SHORT_SEPARATORS, coreapi, coreschema,
     pygments_css, yaml
@@ -343,11 +343,23 @@ def render_field(self, field, parent_style):
         field = field.as_form_field()
 
         if style.get('input_type') == 'datetime-local':
+            # Because DateTimeField.to_representation returns a string,
+            # need to parse it back to datetime for proper formatting
+            has_format = hasattr(field._field, "format")
+
+            if has_format:
+                if field._field.format is None:
+                    datetime_field_value = field.value
+                else:
+                    datetime_field_value = datetime.datetime.strptime(field.value, field._field.format)
+            else:
+                if api_settings.DATETIME_FORMAT == ISO_8601:
+                    datetime_field_value = datetime.datetime.fromisoformat(field.value.rstrip('Z'))
+
             # The format of an input type="datetime-local" is "yyyy-MM-ddThh:mm"
             # followed by optional ":ss" or ":ss.SSS", so keep only the first three
             # digits of milliseconds to avoid browser console error.
-            datetime_value = field._field.parent.validated_data.get(field.field_name)
-            field.value = datetime_value.replace(tzinfo=None).isoformat(timespec="milliseconds").rstrip('Z')
+            field.value = datetime_field_value.replace(tzinfo=None).isoformat(timespec="milliseconds")
 
         if 'template' in style:
             template_name = style['template']

tests/test_renderers.py

@@ -540,6 +540,21 @@ class TestSerializer(serializers.Serializer):
             rendered
         )
 
+    def test_datetime_field_rendering_with_format_as_none(self):
+        class TestSerializer(serializers.Serializer):
+            appointment = serializers.DateTimeField(format=None)
+
+        appointment = datetime(2024, 12, 24, 0, 55, 30, 345678)
+        serializer = TestSerializer(data={"appointment": appointment})
+        serializer.is_valid()
+        renderer = HTMLFormRenderer()
+        field = serializer['appointment']
+        rendered = renderer.render_field(field, {})
+        self.assertInHTML(
+            '<input name="appointment" class="form-control" type="datetime-local" value="2024-12-24T00:55:30.345">',
+            rendered
+        )
+
     def test_datetime_field_rendering_with_format(self):
         class TestSerializer(serializers.Serializer):
             appointment = serializers.DateTimeField(format='%a %d %b %Y, %I:%M%p')
@@ -551,7 +566,7 @@ class TestSerializer(serializers.Serializer):
         field = serializer['appointment']
         rendered = renderer.render_field(field, {})
         self.assertInHTML(
-            '<input name="appointment" class="form-control" type="datetime-local" value="2024-12-24T00:55:30.345">',
+            '<input name="appointment" class="form-control" type="datetime-local" value="2024-12-24T00:55:00.000">',
             rendered
         )