From 47fb5961a3da1c6af784ea08f488372d5f05ab57 Mon Sep 17 00:00:00 2001
From: Michele Bastione <michele.bastione@gmail.com>
Date: Tue, 7 Oct 2025 22:27:29 +0200
Subject: [PATCH] Added custom exception for indexers being treated as
 properties during serialization

---
 .../MiniExcelNotSerializableException.cs       |  7 +++++++
 .../Reflection/MiniExcelProperty.cs            |  8 ++++++++
 .../MiniExcelIssueTests.cs                     | 18 ++++++++++++++++++
 3 files changed, 33 insertions(+)
 create mode 100644 src/MiniExcel.Core/Exceptions/MiniExcelNotSerializableException.cs

diff --git a/src/MiniExcel.Core/Exceptions/MiniExcelNotSerializableException.cs b/src/MiniExcel.Core/Exceptions/MiniExcelNotSerializableException.cs
new file mode 100644
index 00000000..7440bb13
--- /dev/null
+++ b/src/MiniExcel.Core/Exceptions/MiniExcelNotSerializableException.cs
@@ -0,0 +1,7 @@
+namespace MiniExcelLib.Core.Exceptions;
+
+public class MiniExcelNotSerializableException(string message, MemberInfo member) 
+    : InvalidOperationException(message)
+{
+    public MemberInfo Member { get; } = member;
+}
\ No newline at end of file
diff --git a/src/MiniExcel.Core/Reflection/MiniExcelProperty.cs b/src/MiniExcel.Core/Reflection/MiniExcelProperty.cs
index 3c2dafe7..cd1c5fa5 100644
--- a/src/MiniExcel.Core/Reflection/MiniExcelProperty.cs
+++ b/src/MiniExcel.Core/Reflection/MiniExcelProperty.cs
@@ -1,3 +1,5 @@
+using MiniExcelLib.Core.Exceptions;
+
 namespace MiniExcelLib.Core.Reflection;
 
 public abstract class Member;
@@ -12,6 +14,12 @@ public MiniExcelProperty(PropertyInfo property)
         Name = property.Name;
         Info = property;
 
+        if (property.GetIndexParameters().Length != 0)
+        {
+            const string msg = "Types containing indexers cannot be serialized. Please remove them or decorate them with MiniExcelIgnoreAttribute.";
+            throw new MiniExcelNotSerializableException(msg, property);
+        }
+
         if (property.CanRead)
         {
             CanRead = true;
diff --git a/tests/MiniExcel.Core.Tests/MiniExcelIssueTests.cs b/tests/MiniExcel.Core.Tests/MiniExcelIssueTests.cs
index d48ccb9c..9e22e35e 100644
--- a/tests/MiniExcel.Core.Tests/MiniExcelIssueTests.cs
+++ b/tests/MiniExcel.Core.Tests/MiniExcelIssueTests.cs
@@ -3710,4 +3710,22 @@ public void TestIssue876()
             _excelExporter.Export(outputPath.ToString(), sheets);
         });
     }
+
+    private class Issue880
+    {
+        public string Test { get; set; }
+        public string this[int i] => "";
+    }
+    
+    [Fact]
+    public void TestIssue880_ShouldThrowNotSerializableException()
+    {
+        Issue880[] toExport = [new() { Test = "test" }];
+        
+        Assert.Throws<MiniExcelNotSerializableException>(() =>
+        {
+            using var ms = new MemoryStream();
+            _excelExporter.Export(ms, toExport);
+        });
+    }
 }
\ No newline at end of file