Fixing bug in decoder eval for optional fields (#354)

dataclasses_json/core.py

@@ -167,17 +167,23 @@ def _decode_dataclass(cls, kvs, infer_missing):
 
  field_value = kvs[field.name]
  field_type = types[field.name]
- if field_value is None and not _is_optional(field_type):
- warning = (f"value of non-optional type {field.name} detected "
- f"when decoding {cls.__name__}")
- if infer_missing:
- warnings.warn(
- f"Missing {warning} and was defaulted to None by "
- f"infer_missing=True. "
- f"Set infer_missing=False (the default) to prevent this "
- f"behavior.", RuntimeWarning)
- else:
- warnings.warn(f"`NoneType` object {warning}.", RuntimeWarning)
+ if field_value is None:
+ if not _is_optional(field_type):
+ warning = (
+ f"value of non-optional type {field.name} detected "
+ f"when decoding {cls.__name__}"
+ )
+ if infer_missing:
+ warnings.warn(
+ f"Missing {warning} and was defaulted to None by "
+ f"infer_missing=True. "
+ f"Set infer_missing=False (the default) to prevent "
+ f"this behavior.", RuntimeWarning
+ )
+ else:
+ warnings.warn(
+ f"`NoneType` object {warning}.", RuntimeWarning
+ )
  init_kwargs[field.name] = field_value
  continue
 

tests/test_metadata.py

@@ -1,5 +1,6 @@
 import datetime
 from dataclasses import dataclass, field
+from typing import Optional
 
 import pytest
 from marshmallow import fields, ValidationError
@@ -23,10 +24,21 @@ class StringDate(DataClassJsonMixin):
  'decoder': str,
  'mm_field': fields.String(required=False)}
  })
+
+@dataclass
+class OptionalStringDate(DataClassJsonMixin):
+ string_date: Optional[datetime.datetime] = field(
+ default=None,
+ metadata={'dataclasses_json': {
+ 'encoder': str,
+ 'decoder': str,
+ 'mm_field': fields.String(required=False)}
+ })
 
 
 car_schema = Car.schema()
 string_date_schema = StringDate.schema()
+opt_string_date_schema = OptionalStringDate.schema()
 
 
 class TestMetadata:
@@ -39,3 +51,12 @@ def test_mm_field_takes_precedence_over_types(self):
  obj = string_date_schema.load({'string_date': 'yesterday'})
  assert isinstance(obj, StringDate)
  assert obj.string_date == 'yesterday'
+
+ def test_optional_field_only_decoded_when_present(self):
+ obj = opt_string_date_schema.load({})
+ assert isinstance(obj, OptionalStringDate)
+ assert obj.string_date == None
+
+ another_obj = opt_string_date_schema.load({'string_date': 'today'})
+ assert isinstance(another_obj, OptionalStringDate)
+ assert another_obj.string_date == 'today'