From ce3c5d63c4a8d2531e977bbd3424cba8c6bcc73d Mon Sep 17 00:00:00 2001
From: Leonardo Scappatura <95079472+Leonard013@users.noreply.github.com>
Date: Sat, 11 Jul 2026 21:07:59 +0200
Subject: [PATCH] Fix NixIO writing of datetime array_annotations

NixIO._write_property passed datetime/date/time objects contained in
array_annotations straight to nixio.create_property, which cannot store
them and raised "Unknown type for value ...". Convert each datetime item
to its ISO string form via dt_to_nix() on write (mirroring the existing
scalar-annotation path) and record the annotation type as the property
definition. On read, reconstruct multi-element datetime array_annotations
element-wise into an object-dtype ndarray so the write->read roundtrip
preserves them.

Fixes #1198

Co-authored-by: Claude <noreply@anthropic.com>
---
 neo/io/nixio.py               |  7 ++++++-
 neo/test/iotest/test_nixio.py | 23 +++++++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/neo/io/nixio.py b/neo/io/nixio.py
index 2922138f8..19c991644 100644
--- a/neo/io/nixio.py
+++ b/neo/io/nixio.py
@@ -1261,6 +1261,8 @@ def _write_property(self, section, name, v):
                 for item in v:
                     if isinstance(item, str):
                         item = item
+                    elif isinstance(item, datetime_types):
+                        item, definition = dt_to_nix(item)
                     elif isinstance(item, pq.Quantity):
                         current_unit = str(item.dimensionality)
                         if unit is None:
@@ -1320,7 +1322,10 @@ def _nix_attr_to_neo(nix_obj):
                     units = prop.unit
                     values = create_quantity(values, units)
                 if prop.definition in (DATEANNOTATION, TIMEANNOTATION, DATETIMEANNOTATION):
-                    values = dt_from_nix(values, prop.definition)
+                    if isinstance(values, list):
+                        values = np.array([dt_from_nix(v, prop.definition) for v in values], dtype=object)
+                    else:
+                        values = dt_from_nix(values, prop.definition)
                 if prop.type == ARRAYANNOTATION:
                     if "array_annotations" in neo_attrs:
                         neo_attrs["array_annotations"][prop.name] = values
diff --git a/neo/test/iotest/test_nixio.py b/neo/test/iotest/test_nixio.py
index fdcf39529..2986ca660 100644
--- a/neo/test/iotest/test_nixio.py
+++ b/neo/test/iotest/test_nixio.py
@@ -1362,6 +1362,29 @@ def test_empty_array_annotations(self):
             else:
                 self.assertFalse(hasattr(rst.array_annotations[k], "units"))
 
+    def test_datetime_array_annotations(self):
+        # Regression test for GH Issue #1198: array_annotations holding
+        # datetime/date/time objects must survive a NixIO write/read roundtrip
+        wblock = Block("block with datetime array annotations")
+        wseg = Segment()
+        times = np.array([1.0, 2.0, 3.0]) * pq.s
+        datetime_array_annotations = {
+            "acq_datetime": np.array(
+                [datetime(2021, 1, 1, 0, 0, 0), datetime(2021, 6, 15, 12, 30, 0), datetime(2022, 3, 3, 8, 15, 30)],
+                dtype=object,
+            ),
+            "acq_date": np.array([date(2021, 1, 1), date(2021, 6, 15), date(2022, 3, 3)], dtype=object),
+            "acq_time": np.array([time(0, 0, 0), time(12, 30, 0), time(8, 15, 30)], dtype=object),
+        }
+        wseg.events = [Event(times=times, array_annotations=datetime_array_annotations)]
+        wblock.segments = [wseg]
+        self.writer.write_block(wblock)
+        rblock = self.writer.read_block(neoname="block with datetime array annotations")
+        revent = rblock.segments[0].events[0]
+        for k, v in datetime_array_annotations.items():
+            self.assertIn(k, revent.array_annotations)
+            np.testing.assert_array_equal(revent.array_annotations[k], v)
+
     def test_write_proxyobjects(self):
 
         def generate_complete_block():