fix(TimedeltaField): fix timedelta fastavro serialization so it doesn…

…'t break in union types (#797)

Fastavro [custom logical type encoders](https://fastavro.readthedocs.io/en/latest/logical_types.html#custom-logical-types) should explicitly check that they are operating on the expected python type before encoding it, and return the unchanged data otherwise. If a custom logical type is used as a member of a union type, then this encoder function will be called on any value that is provided for a field of that type, even if the value's type is a different member of the union type.

dataclasses_avroschema/fields/fields.py

@@ -679,21 +679,36 @@ def default_to_avro(self, value: datetime.timedelta) -> float:
         return self.to_avro(value)
 
     @classmethod
-    def from_avro(cls, value: float, *_) -> datetime.timedelta:
+    def from_avro(cls, value: float) -> datetime.timedelta:
         """Convert from a fastavro-supported type to a timedelta."""
         return datetime.timedelta(seconds=value)
 
     @classmethod
-    def to_avro(cls, value: datetime.timedelta, *_) -> float:
+    def to_avro(cls, value: datetime.timedelta) -> float:
         """Convert from a timedelta to a fastavro-supported type."""
         return value.total_seconds()
 
     def fake(self) -> datetime.timedelta:
         return fake.time_delta(end_datetime=fake.date_time())
 
 
-fastavro.write.LOGICAL_WRITERS["double-dataclasses-avroschema-timedelta"] = TimedeltaField.to_avro
-fastavro.read.LOGICAL_READERS["double-dataclasses-avroschema-timedelta"] = TimedeltaField.from_avro
+def _fastavro_serialize_timedelta(data: typing.Any, *_) -> typing.Any:
+    """Serialize a timedelta for fastavro."""
+    # Fastavro will call this function on any value that is provided for a
+    # union type where one of the union members is a timedelta, so we have to
+    # explicitly check if the value is a timedelta before trying to convert it.
+    if isinstance(data, datetime.timedelta):
+        return TimedeltaField.to_avro(data)
+    return data
+
+
+def _fastavro_deserialize_timedelta(data: float, *_) -> datetime.timedelta:
+    """Deserialize a timedelta for fastavro."""
+    return TimedeltaField.from_avro(data)
+
+
+fastavro.write.LOGICAL_WRITERS["double-dataclasses-avroschema-timedelta"] = _fastavro_serialize_timedelta
+fastavro.read.LOGICAL_READERS["double-dataclasses-avroschema-timedelta"] = _fastavro_deserialize_timedelta
 
 
 @dataclasses.dataclass

tests/serialization/test_logical_types_serialization.py

@@ -82,13 +82,16 @@ class UnionSchema(model_class):
         "Some Unions"
 
         logical_union: typing.Union[datetime.datetime, datetime.date, uuid.UUID]
+        logical_union_timedelta: typing.Union[datetime.timedelta, None]
 
     data = {
         "logical_union": a_datetime.date(),
+        "logical_union_timedelta": None,
     }
 
     data_json = {
         "logical_union": serialization.date_to_str(a_datetime.date()),
+        "logical_union_timedelta": None,
     }
 
     logical_types = UnionSchema(**data)