Merge pull request #166 from jacebrowning/fix-optional-dataclass-serialization

Fix serialization of optional nested dataclasses

Author: jacebrowning

CHANGELOG.md

@@ -1,3 +1,7 @@
+# 0.9 (beta)
+
+- Fixed serialization of optional nested dataclasses with a value of `None`.
+
 # 0.8.1 (2020-03-30)
 
 - Fixed loading of `Missing` nested dataclasses attributes.

datafiles/converters/_bases.py

@@ -7,7 +7,7 @@ class Converter:
     """Base class for immutable attribute conversion."""
 
     TYPE: type = object
-    DEFAULT: Any = None
+    DEFAULT: Any = NotImplemented
 
     @classmethod
     def as_optional(cls):

datafiles/converters/containers.py

@@ -171,19 +171,22 @@ def to_python_value(cls, deserialized_data, *, target_object):
     def to_preserialization_data(cls, python_value, *, default_to_skip=None):
         data = {}
 
+        if python_value is None and cls.DEFAULT is None:
+            return None
+
         for name, converter in cls.CONVERTERS.items():
 
             if isinstance(python_value, dict):
                 try:
                     value = python_value[name]
-                except KeyError as e:
-                    log.debug(e)
+                except KeyError:
+                    log.debug(f'Added missing nested attribute: {name}')
                     value = None
             else:
                 try:
                     value = getattr(python_value, name)
-                except AttributeError as e:
-                    log.debug(e)
+                except AttributeError:
+                    log.debug(f'Added missing nested attribute: {name}')
                     value = None
 
             with suppress(AttributeError):

datafiles/mapper.py

@@ -138,14 +138,6 @@ def _get_data(self, include_default_values: Trilean = None) -> Dict:
 
             if getattr(converter, 'DATACLASS', None):
                 log.debug(f"Converting '{name}' dataclass with {converter}")
-                if value is None:
-                    value = {}
-
-                for field in dataclasses.fields(converter.DATACLASS):
-                    if field.name not in value:
-                        log.debug(f'Added missing nested attribute: {field.name}')
-                        value[field.name] = None
-
                 data[name] = converter.to_preserialization_data(
                     value,
                     default_to_skip=Missing

datafiles/tests/test_converters.py

@@ -146,11 +146,6 @@ def when_immutable(expect, converter, data, value):
                 (MyDataclassConverter, None, MyDataclass(foobar=0)),
                 (MyDataclassConverterList, None, []),
                 (MyDataclassConverterList, 42, [MyDataclass(foobar=0)]),
-                (
-                    MyNestedDataclassConverter,
-                    None,
-                    MyNestedDataclass(name='', dc=MyDataclass(foobar=0, flag=False)),
-                ),
             ],
         )
         def when_mutable(expect, converter, data, value):

poetry.lock

@@ -1,7 +1,7 @@
 [tool.poetry]
 
 name = "datafiles"
-version = "0.8.1"
+version = "0.9b1"
 description = "File-based ORM for dataclasses."
 
 license = "MIT"

pyproject.toml

@@ -2,8 +2,11 @@
 
 # pylint: disable=unused-variable,assigning-non-slot
 
+from typing import Optional
+
 import pytest
 
+from datafiles import datafile
 from datafiles.utils import dedent, logbreak, read, write
 
 from .samples import (
@@ -224,6 +227,26 @@ def with_nones(expect):
             """
         )
 
+    def when_nested_dataclass_is_none(expect):
+        @datafile
+        class Name:
+            value: str
+
+        @datafile("../tmp/samples/{self.key}.yml")
+        class Sample:
+
+            key: int
+            name: Optional[Name]
+            value: float = 0.0
+
+        sample = Sample(42, None)
+
+        expect(read('tmp/samples/42.yml')) == dedent(
+            """
+            name:
+            """
+        )
+
 
 def describe_defaults():
     def with_custom_values(expect):