A fix to allow nullable fields.nested for input validation. (#640)

Co-authored-by: Peter Doggart <peter.doggart@pulseai.io>

Author: peter-doggart

CHANGELOG.rst

@@ -35,9 +35,9 @@ Bug Fixes
 ::
 
    * Add python version requirement on setup.py (#586) [jason-the-j]
+   * Fix Nested field schema generation for nullable fields. (#638) [peter-doggart]
    * Fix reference resolution for definitions in schema. (#553) [peter-doggart]
 
-
 .. _section-1.3.0:
 1.3.0
 -----

flask_restx/fields.py

@@ -134,6 +134,9 @@ class Raw(object):
     :param bool readonly: Is the field read only ? (for documentation purpose)
     :param example: An optional data example (for documentation purpose)
     :param callable mask: An optional mask function to be applied to output
+    :param bool nullable: Whether the field accepts null values in input
+        validation. When True, the generated JSON Schema will allow null
+        values for this field during request payload validation.
     """
 
     #: The JSON/Swagger schema type
@@ -153,6 +156,7 @@ def __init__(
         readonly=None,
         example=None,
         mask=None,
+        nullable=None,
         **kwargs
     ):
         self.attribute = attribute
@@ -163,6 +167,7 @@ def __init__(
         self.readonly = readonly
         self.example = example if example is not None else self.__schema_example__
         self.mask = mask
+        self.nullable = nullable
 
     def format(self, value):
         """
@@ -284,6 +289,19 @@ def schema(self):
             schema["allOf"] = allOf
         else:
             schema["$ref"] = ref
+
+        # If nullable is True, wrap using anyOf to permit nulls for input validation
+        if self.nullable:
+            # Remove structural keys that conflict with anyOf composition
+            for key in ("$ref", "allOf", "type", "items"):
+                schema.pop(key, None)
+            # Create anyOf with the original schema and null type
+            anyOf = [{"$ref": ref}]
+            if self.as_list:
+                anyOf = [{"type": "array", "items": {"$ref": ref}}]
+            anyOf.append({"type": "null"})
+            schema["anyOf"] = anyOf
+
         return schema
 
     def clone(self, mask=None):

tests/test_fields.py

@@ -881,6 +881,17 @@ def test_with_allow_null(self, api):
         assert field.allow_null
         assert field.__schema__ == {"$ref": "#/definitions/NestedModel"}
 
+    def test_with_nullable_schema(self, api):
+        nested_fields = api.model("NestedModel", {"name": fields.String})
+        field = fields.Nested(nested_fields, nullable=True)
+        # Should allow null in schema via anyOf
+        assert field.__schema__ == {
+            "anyOf": [
+                {"$ref": "#/definitions/NestedModel"},
+                {"type": "null"},
+            ]
+        }
+
     def test_with_skip_none(self, api):
         nested_fields = api.model("NestedModel", {"name": fields.String})
         field = fields.Nested(nested_fields, skip_none=True)