fix(client): preserve prepared null parameter types

src/altertable_flightsql/client.py

@@ -697,7 +697,18 @@ def _get_parameter_as_pyarrow(
         elif isinstance(parameters, pa.RecordBatch):
             return parameters
         elif isinstance(parameters, Mapping):
-            return pa.record_batch({key: [value] for (key, value) in parameters.items()})
+            return pa.RecordBatch.from_pydict(
+                {
+                    key: (
+                        pa.array([value], type=self._parameter_schema.field(key).type)
+                        if value is None
+                        and self._parameter_schema is not None
+                        and key in self._parameter_schema.names
+                        else [value]
+                    )
+                    for key, value in parameters.items()
+                }
+            )
         elif isinstance(parameters, Sequence):
             if self._parameter_schema is None:
                 raise ValueError(
@@ -711,10 +722,11 @@ def _get_parameter_as_pyarrow(
                     f"Expected {len(self._parameter_schema)} parameters, but got {len(parameters)}"
                 )
             param_dict = {
-                field.name: [value] for field, value in zip(self._parameter_schema, parameters)
+                field.name: pa.array([value], type=field.type) if value is None else [value]
+                for field, value in zip(self._parameter_schema, parameters)
             }
 
-            return pa.record_batch(param_dict)
+            return pa.RecordBatch.from_pydict(param_dict)
         else:
             raise TypeError(
                 f"Unsupported parameter type: {type(parameters)}. "

tests/test_client.py

@@ -1,10 +1,11 @@
 from types import SimpleNamespace
 
+import pyarrow as pa
 import pyarrow.flight as flight
 import pytest
 from google.protobuf import any_pb2
 
-from altertable_flightsql.client import Client
+from altertable_flightsql.client import Client, PreparedStatement
 from altertable_flightsql.generated import arrow_flight_pb2 as flight_pb2
 
 
@@ -69,6 +70,24 @@ def _action_body_bytes(action) -> bytes:
     return bytes(body)
 
 
+@pytest.mark.parametrize(
+    "values",
+    [
+        [None],
+        {"amount": None},
+    ],
+    ids=["positional", "mapping"],
+)
+def test_python_null_parameters_use_prepared_type(values):
+    parameter_schema = pa.schema([("amount", pa.float64())])
+    statement = PreparedStatement(None, b"handle", parameter_schema=parameter_schema)
+
+    parameters = statement._get_parameter_as_pyarrow(values)
+
+    assert parameters.schema.equals(parameter_schema)
+    assert parameters.to_pydict() == {"amount": [None]}
+
+
 def test_set_options_serializes_flight_session_request_without_any():
     flight_client = FakeFlightClient()
     client = _client_backed_by(flight_client)