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feat: add default parameter to JsonObject.serialize() #1508

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feat: add default parameter to JsonObject.serialize() #1508

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29 changes: 24 additions & 5 deletions google/cloud/spanner_v1/data_types.py
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Original file line number Diff line number Diff line change
Expand Up @@ -80,22 +80,41 @@ def from_str(cls, str_repr):

return cls(json.loads(str_repr))

def serialize(self):
def serialize(self, default=None):
"""Return the object text representation.

Args:
default (callable, optional): A function that is called for
objects that are not JSON serializable. It should return a
JSON-encodable version of the object or raise a
:class:`TypeError`. This is passed directly to
:func:`json.dumps` as the ``default`` parameter.
For example, to support ``datetime`` objects::

obj.serialize(default=lambda o: o.isoformat()
if hasattr(o, 'isoformat') else str(o))
Comment on lines +94 to +95
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@gemini-code-assist gemini-code-assist bot Feb 28, 2026

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medium

The example default function can lead to subtle bugs. The else str(o) clause will convert any unhandled non-serializable object into its string representation (e.g., '<MyObject object at 0x...>'), which might not be the desired behavior and can mask serialization errors. A more robust approach is to handle only the expected types and let other types raise a TypeError, which is the standard behavior of json.dumps.

Consider providing a more explicit example that promotes this safer pattern, even if it's more verbose:

# In a scope where `datetime` is imported
def custom_serializer(obj):
    if isinstance(obj, (datetime.date, datetime.datetime)):
        return obj.isoformat()
    raise TypeError(f'Object of type {type(obj).__name__} is not JSON serializable')

obj.serialize(default=custom_serializer)


Returns:
str: JSON object text representation.
str: JSON object text representation, or None if the object
is null.
"""
if self._is_null:
return None

if self._is_scalar_value:
return json.dumps(self._simple_value)
return json.dumps(self._simple_value, default=default)

if self._is_array:
return json.dumps(self._array_value, sort_keys=True, separators=(",", ":"))
return json.dumps(
self._array_value,
sort_keys=True,
separators=(",", ":"),
default=default,
)

return json.dumps(self, sort_keys=True, separators=(",", ":"))
return json.dumps(
self, sort_keys=True, separators=(",", ":"), default=default
)


@dataclass
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48 changes: 48 additions & 0 deletions tests/unit/test_datatypes.py
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Expand Up @@ -96,3 +96,51 @@ def test_w_JsonObject_of_list_of_simple_JsonData(self):
expected = json.dumps(data, sort_keys=True, separators=(",", ":"))
data_jsonobject = JsonObject(JsonObject(data))
self.assertEqual(data_jsonobject.serialize(), expected)


class Test_JsonObject_serialize_default(unittest.TestCase):
"""Tests for the ``default`` parameter of ``JsonObject.serialize()``."""

def test_dict_with_custom_type_and_default(self):
from datetime import datetime

dt = datetime(2023, 6, 15, 9, 30, 0)
data = {"ts": dt, "name": "test"}
obj = JsonObject(data)
result = obj.serialize(default=lambda o: o.isoformat() if isinstance(o, datetime) else str(o))
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medium

This lambda function is repeated in test_array_with_custom_type_and_default and test_scalar_with_default. To improve maintainability and readability, consider defining it once at the test class level and reusing it across these tests.

For example:

class Test_JsonObject_serialize_default(unittest.TestCase):
    _DATETIME_SERIALIZER = lambda o: o.isoformat() if isinstance(o, datetime) else str(o)

    def test_dict_with_custom_type_and_default(self):
        # ...
        result = obj.serialize(default=self._DATETIME_SERIALIZER)
        # ...

parsed = json.loads(result)
self.assertEqual(parsed["ts"], "2023-06-15T09:30:00")
self.assertEqual(parsed["name"], "test")

def test_array_with_custom_type_and_default(self):
from datetime import datetime

dt = datetime(2023, 1, 1)
data = [dt, "hello"]
obj = JsonObject(data)
result = obj.serialize(default=lambda o: o.isoformat() if isinstance(o, datetime) else str(o))
parsed = json.loads(result)
self.assertEqual(parsed[0], "2023-01-01T00:00:00")
self.assertEqual(parsed[1], "hello")

def test_without_default_raises_on_custom_type(self):
from datetime import datetime

data = {"ts": datetime(2023, 1, 1)}
obj = JsonObject(data)
with self.assertRaises(TypeError):
obj.serialize()

def test_default_none_preserves_existing_behavior(self):
data = {"foo": "bar"}
expected = json.dumps(data, sort_keys=True, separators=(",", ":"))
obj = JsonObject(data)
self.assertEqual(obj.serialize(default=None), expected)

def test_scalar_with_default(self):
from datetime import datetime

dt = datetime(2023, 6, 15)
obj = JsonObject(dt)
result = obj.serialize(default=lambda o: o.isoformat() if isinstance(o, datetime) else str(o))
self.assertEqual(json.loads(result), "2023-06-15T00:00:00")
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