Add DateTime to DateOnly conversion

src/MiniExcel.Core/Enums/DateOnlyConversionMode.cs

@@ -0,0 +1,20 @@
+namespace MiniExcelLib.Core.Enums;
+
+
+public enum DateOnlyConversionMode
+{
+    /// <summary>
+    /// No conversion is applied and DateOnly values are not transformed.
+    /// </summary>
+    None,
+
+    /// <summary>
+    /// Allows conversion from DateTime to DateOnly only if the time component is exactly midnight (00:00:00).
+    /// </summary>
+    RequireMidnight,
+
+    /// <summary>
+    /// Converts DateTime to DateOnly by ignoring the time part completely, assuming the time component is not critical.
+    /// </summary>
+    IgnoreTimePart
+}

src/MiniExcel.Core/MiniExcelConfiguration.cs

@@ -1,4 +1,5 @@
 using MiniExcelLib.Core.Attributes;
+using MiniExcelLib.Core.Enums;
 
 namespace MiniExcelLib.Core;
 
@@ -15,4 +16,9 @@ public abstract class MiniExcelBaseConfiguration : IMiniExcelConfiguration
     /// When exporting using DataReader, the data not in DynamicColumn will be filtered.
     /// </summary>
     public bool DynamicColumnFirst { get; set; } = false;
+
+    /// <summary>
+    /// Specifies when and how DateTime values are converted to DateOnly values.
+    /// </summary>
+    public DateOnlyConversionMode DateOnlyConversionMode { get; set; }
 }

src/MiniExcel.Core/Reflection/MiniExcelMapper.cs

@@ -1,4 +1,5 @@
 using System.ComponentModel;
+using MiniExcelLib.Core.Enums;
 using MiniExcelLib.Core.Exceptions;
 
 namespace MiniExcelLib.Core.Reflection;
@@ -27,7 +28,7 @@
                 headersDic = CustomPropertyHelper.GetHeaders(item, trimColumnNames);
 
                 //TODO: alert don't duplicate column name
                 props = CustomPropertyHelper.GetExcelCustomPropertyInfos(type, keys, configuration);
                 first = false;
 
                 // if we treat the header as data we move forwards with the mapping otherwise we jump to the next iteration
@@ -150,6 +151,14 @@
                     return newValue;
                 }
 
+                if (itemValue is DateTime dateTimeValue && config.DateOnlyConversionMode is not DateOnlyConversionMode.None)
+                {
+                    if (config.DateOnlyConversionMode == DateOnlyConversionMode.RequireMidnight && dateTimeValue.TimeOfDay != TimeSpan.Zero)
+                        throw new InvalidCastException($"Could not convert cell of type DateTime to DateOnly, because DateTime was not at midnight, but at {dateTimeValue:HH:mm:ss}.");
+
+                    return DateOnly.FromDateTime(dateTimeValue);
+                }
+
                 var vs = itemValue?.ToString();
                 if (pInfo.ExcelFormat is not null)
                 {

tests/MiniExcel.Core.Tests/MiniExcelIssueTests.cs

@@ -1,5 +1,6 @@
 using System.ComponentModel;
 using System.Text.RegularExpressions;
+using MiniExcelLib.Core.Enums;
 using MiniExcelLib.Core.Exceptions;
 using MiniExcelLib.Core.OpenXml.Picture;
 using MiniExcelLib.Core.OpenXml.Utils;
@@ -16,9 +17,7 @@ public class MiniExcelIssueTests(ITestOutputHelper output)
     private readonly OpenXmlExporter _excelExporter =  MiniExcel.Exporters.GetOpenXmlExporter();
     private readonly OpenXmlTemplater _excelTemplater =  MiniExcel.Templaters.GetOpenXmlTemplater();
 
-    // private readonly OpenXmlImporter _csvImporter =  MiniExcel.Importer.GetCsvImporter();
-    // private readonly OpenXmlExporter _csvExporter =  MiniExcel.Exporter.GetCsvExporter();
-
+
     /// <summary>
     /// https://github.com/mini-software/MiniExcel/issues/549
     /// </summary>
@@ -3653,4 +3652,41 @@ public void TestIssue809()
         Assert.Equal(null, rows[0].A);
         Assert.Equal(2, rows[2].B);
     }
+
+
+    private class Issue869
+    {
+        public string? Name { get; set; }
+        public DateOnly? Date { get; set; }
+    }
+
+    [Theory]
+    [InlineData("DateTimeMidnight", DateOnlyConversionMode.None, true)]
+    [InlineData("DateTimeNotMidnight", DateOnlyConversionMode.None, true)]
+    [InlineData("DateTimeMidnight", DateOnlyConversionMode.RequireMidnight, false)]
+    [InlineData("DateTimeNotMidnight", DateOnlyConversionMode.RequireMidnight, true)]
+    [InlineData("DateTimeMidnight", DateOnlyConversionMode.IgnoreTimePart, false)]
+    [InlineData("DateTimeNotMidnight", DateOnlyConversionMode.IgnoreTimePart, false)]
+    public void TestIssue869(string fileName, DateOnlyConversionMode mode, bool throwsException)
+    {
+        var path = PathHelper.GetFile($"xlsx/TestIssue869/{fileName}.xlsx");
+        var config = new OpenXmlConfiguration { DateOnlyConversionMode = mode };
+
+        var testFn = () => _excelImporter.Query<Issue869>(path, configuration: config).ToList();
+        if (throwsException)
+        {
+            Assert.Throws<MiniExcelInvalidCastException>(testFn);
+        }
+        else
+        {
+            try
+            {
+                _ = testFn();
+            }
+            catch (Exception ex)
+            {
+                Assert.Fail($"No exception should be thrown, but one was still thrown: {ex}.");
+            }
+        }
+    }
 }