Bugfix: support writing NAT in datetime column

CHANGES.md

@@ -5,6 +5,7 @@
 ### Bug fixes
 
 -   register GDAL drivers during initial import of pyogrio (#145)
+-   support writing "not a time" (NaT) values in a datetime column (#146)
 
 ## 0.4.1
 

pyogrio/_io.pyx

@@ -1407,33 +1407,39 @@ def ogr_write(str path, str layer, str driver, geometry, field_data, fields,
                     OGR_F_SetFieldDouble(ogr_feature, field_idx, field_value)
 
                 elif field_type == OFTDate:
-                    datetime = field_value.item()
-                    OGR_F_SetFieldDateTimeEx(
-                        ogr_feature,
-                        field_idx,
-                        datetime.year,
-                        datetime.month,
-                        datetime.day,
-                        0,
-                        0,
-                        0.0,
-                        0
-                    )
+                    if np.isnat(field_value):
+                        OGR_F_SetFieldNull(ogr_feature, field_idx)
+                    else:
+                        datetime = field_value.item()
+                        OGR_F_SetFieldDateTimeEx(
+                            ogr_feature,
+                            field_idx,
+                            datetime.year,
+                            datetime.month,
+                            datetime.day,
+                            0,
+                            0,
+                            0.0,
+                            0
+                        )
 
                 elif field_type == OFTDateTime:
-                    # TODO: add support for timezones
-                    datetime = field_value.astype("datetime64[ms]").item()
-                    OGR_F_SetFieldDateTimeEx(
-                        ogr_feature,
-                        field_idx,
-                        datetime.year,
-                        datetime.month,
-                        datetime.day,
-                        datetime.hour,
-                        datetime.minute,
-                        datetime.second + datetime.microsecond / 10**6,
-                        0
-                    )
+                    if np.isnat(field_value):
+                        OGR_F_SetFieldNull(ogr_feature, field_idx)
+                    else:
+                        # TODO: add support for timezones
+                        datetime = field_value.astype("datetime64[ms]").item()
+                        OGR_F_SetFieldDateTimeEx(
+                            ogr_feature,
+                            field_idx,
+                            datetime.year,
+                            datetime.month,
+                            datetime.day,
+                            datetime.hour,
+                            datetime.minute,
+                            datetime.second + datetime.microsecond / 10**6,
+                            0
+                        )
 
                 else:
                     raise NotImplementedError(f"OGR field type is not supported for writing: {field_type}")

pyogrio/tests/test_raw_io.py

@@ -437,13 +437,16 @@ def test_read_write_datetime(tmp_path):
             ["2001-01-01T12:00", "2002-02-03T13:56:03.072123456"],
             dtype="datetime64[ns]",
         ),
+        # Remark: a None value is automatically converted to np.datetime64("NaT")
+        np.array([np.datetime64("NaT"), None], dtype="datetime64[ms]"),
     ]
     fields = [
         "datetime64_d",
         "datetime64_s",
         "datetime64_ms",
         "datetime64_ns",
         "datetime64_precise_ns",
+        "datetime64_ms_nat",
     ]
 
     # Point(0, 0)
@@ -460,7 +463,7 @@ def test_read_write_datetime(tmp_path):
             # gdal rounds datetimes to ms
             assert np.array_equal(result[idx], field_data[idx].astype("datetime64[ms]"))
         else:
-            assert np.array_equal(result[idx], field_data[idx])
+            assert np.array_equal(result[idx], field_data[idx], equal_nan=True)
 
 
 def test_read_data_types_numeric_with_null(test_gpkg_nulls):