Add check and conversion for datetime (#12998)

Author: frode-aarstad

src/ert/config/design_matrix.py

@@ -9,6 +9,8 @@
 import polars as pl
 from polars.exceptions import InvalidOperationError
 
+from ert.config.parsing.config_errors import ConfigWarning
+
 from .distribution import RawSettings
 from .gen_kw_config import DataSource, GenKwConfig
 from .parsing import ConfigValidationError, ErrorInfo
@@ -239,6 +241,25 @@ def read_and_validate_design_matrix(
         )
         if design_matrix_df.is_empty():
             raise ValueError("Design sheet body is empty.")
+
+        # Design matrix does not support datetime columns,
+        # so we convert them to strings and warn the user.
+        datetime_cols = design_matrix_df.select(pl.col(pl.Date, pl.Datetime)).columns
+        if len(datetime_cols) > 0:
+            datetime_col_indices = [
+                design_matrix_df.columns.index(col) for col in datetime_cols
+            ]
+            affected_param_names = [param_names[i] for i in datetime_col_indices]
+            ConfigWarning.warn(
+                "The design matrix contains date/datetime columns which are not "
+                "supported and will be converted to strings for internal use. "
+                "The following columns will be converted to strings: "
+                f"{', '.join(map(str, affected_param_names))}."
+            )
+            design_matrix_df = design_matrix_df.with_columns(
+                pl.col(pl.Date, pl.Datetime).cast(pl.String)
+            )
+
         string_cols = [
             col for col, dtype in design_matrix_df.schema.items() if dtype == pl.String
         ]

tests/ert/unit_tests/sensitivity_analysis/test_design_matrix.py

@@ -1,10 +1,13 @@
+from datetime import date, datetime
+
 import numpy as np
 import polars as pl
 import pytest
 from xlsxwriter import Workbook
 
 from ert.config import DataSource, DesignMatrix, GenKwConfig
 from ert.config.design_matrix import DESIGN_MATRIX_GROUP
+from ert.config.parsing.config_errors import ConfigWarning
 from tests.ert.conftest import _create_design_matrix
 
 
@@ -545,3 +548,33 @@ def test_that_numeric_string_columns_are_converted(tmp_path):
     np.testing.assert_equal(df["a"], np.array([1, 2, 3]))
     np.testing.assert_equal(df["b"], np.array([0, 2.2, 0.1]))
     np.testing.assert_equal(df["c"], np.array(["10", "high", "medium"]))
+
+
+def test_that_excel_datetime_columns_are_converted_to_strings_with_warning(tmp_path):
+    design_path = tmp_path / "design_matrix.xlsx"
+    with Workbook(design_path) as wb:
+        ws = wb.add_worksheet("DesignSheet")
+        date_format = wb.add_format({"num_format": "yyyy-mm-dd"})
+
+        ws.write(0, 0, "REAL")
+        ws.write(0, 1, "date_col")
+        ws.write(0, 2, "value")
+
+        ws.write(1, 0, 0)
+        ws.write_datetime(1, 1, date(2026, 3, 1), date_format)  # type: ignore[arg-type]
+        ws.write(1, 2, 1.5)
+
+        ws.write(2, 0, 1)
+        ws.write_datetime(2, 1, datetime(2026, 3, 2, 10, 30), date_format)
+        ws.write(2, 2, 2.5)
+
+    with pytest.warns(
+        ConfigWarning,
+        match="The design matrix contains date/datetime columns",
+    ):
+        design_matrix = DesignMatrix(design_path, "DesignSheet", None)
+
+    df = design_matrix.design_matrix_df
+    assert df.schema["date_col"] == pl.String
+    assert "2026-03-01" in df["date_col"][0]
+    assert "2026-03-02" in df["date_col"][1]