feat: Serialize complex properties as JSON in Application Insights custom dimensions

Directory.Packages.props

@@ -7,6 +7,7 @@
   <ItemGroup Label="Runtime">
     <PackageVersion Include="Microsoft.ApplicationInsights" Version="2.23.0" />
     <PackageVersion Include="NLog" Version="5.5.0" />
+    <PackageVersion Include="System.Text.Json" Version="8.0.5" />
   </ItemGroup>
   <ItemGroup Label="Test">
     <PackageVersion Include="WireMock.Net" Version="1.6.9" />

src/NLogTarget/NLogTarget.csproj

@@ -16,6 +16,7 @@
   <ItemGroup>
     <PackageReference Include="NLog" />
     <PackageReference Include="Microsoft.ApplicationInsights" />
+    <PackageReference Include="System.Text.Json" />
   </ItemGroup>
 
   <Import Project="..\CommonShared\CommonShared.projitems" Label="Shared" />

src/NLogTarget/StringDictionaryConverter.cs

@@ -10,6 +10,7 @@ namespace Microsoft.ApplicationInsights.NLogTarget
     using System;
     using System.Collections;
     using System.Collections.Generic;
+    using System.Text.Json;
 
     /// <summary>
     /// Converts from NLog Object-properties to ApplicationInsight String-properties
@@ -101,7 +102,31 @@ private static string SafeValueConverter(object value)
         {
             try
             {
-                return Convert.ToString(value, System.Globalization.CultureInfo.InvariantCulture);
+                if (value == null)
+                {
+                    return string.Empty;
+                }
+
+                // Handle primitive types and strings directly
+                if (value is string str)
+                {
+                    return str;
+                }
+
+                // Check if the value is a primitive type or a simple type that Convert.ToString handles well
+                var type = value.GetType();
+                if (type.IsPrimitive || type.IsEnum || value is decimal || value is DateTime || value is DateTimeOffset || value is Guid || value is TimeSpan)
+                {
+                    return Convert.ToString(value, System.Globalization.CultureInfo.InvariantCulture);
+                }
+
+                // For complex objects, serialize to JSON
+                return JsonSerializer.Serialize(value, new JsonSerializerOptions
+                {
+                    WriteIndented = false,
+                    PropertyNamingPolicy = null,
+                    DefaultIgnoreCondition = System.Text.Json.Serialization.JsonIgnoreCondition.Never
+                });
             }
             catch
             {

src/NLogTarget/packages.lock.json

@@ -26,6 +26,28 @@
         "resolved": "5.5.0",
         "contentHash": "FCH8s7GWlonH5JXV9/EpeNJ8pRZQMVZOSWX3JrHPU8rzdHJhS5+lUGGvJIUOtzkGV1clYBFR0WXOI5FnUwVCMA=="
       },
+      "System.Text.Json": {
+        "type": "Direct",
+        "requested": "[8.0.5, )",
+        "resolved": "8.0.5",
+        "contentHash": "0f1B50Ss7rqxXiaBJyzUu9bWFOO2/zSlifZ/UNMdiIpDYe4cY4LQQicP4nirK1OS31I43rn062UIJ1Q9bpmHpg==",
+        "dependencies": {
+          "Microsoft.Bcl.AsyncInterfaces": "8.0.0",
+          "System.Buffers": "4.5.1",
+          "System.Memory": "4.5.5",
+          "System.Runtime.CompilerServices.Unsafe": "6.0.0",
+          "System.Text.Encodings.Web": "8.0.0",
+          "System.Threading.Tasks.Extensions": "4.5.4"
+        }
+      },
+      "Microsoft.Bcl.AsyncInterfaces": {
+        "type": "Transitive",
+        "resolved": "8.0.0",
+        "contentHash": "3WA9q9yVqJp222P3x1wYIGDAkpjAku0TMUaaQV22g6L67AI0LdOIrVS7Ht2vJfLHGSPVuqN94vIr15qn+HEkHw==",
+        "dependencies": {
+          "System.Threading.Tasks.Extensions": "4.5.4"
+        }
+      },
       "Microsoft.NETCore.Platforms": {
         "type": "Transitive",
         "resolved": "1.1.0",
@@ -47,8 +69,8 @@
       },
       "System.Memory": {
         "type": "Transitive",
-        "resolved": "4.5.4",
-        "contentHash": "1MbJTHS1lZ4bS4FmsJjnuGJOu88ZzTT2rLvrhW7Ygic+pC0NWA+3hgAen0HRdsocuQXCkUTdFn9yHJJhsijDXw==",
+        "resolved": "4.5.5",
+        "contentHash": "XIWiDvKPXaTveaB7HVganDlOCRoj03l+jrwNvcge/t8vhGYKvqV+dMv6G4SAX2NoNmN0wZfVPTAlFwZcZvVOUw==",
         "dependencies": {
           "System.Buffers": "4.5.1",
           "System.Numerics.Vectors": "4.4.0",
@@ -62,8 +84,26 @@
       },
       "System.Runtime.CompilerServices.Unsafe": {
         "type": "Transitive",
-        "resolved": "5.0.0",
-        "contentHash": "ZD9TMpsmYJLrxbbmdvhwt9YEgG5WntEnZ/d1eH8JBX9LBp+Ju8BSBhUGbZMNVHHomWo2KVImJhTDl2hIgw/6MA=="
+        "resolved": "6.0.0",
+        "contentHash": "/iUeP3tq1S0XdNNoMz5C9twLSrM/TH+qElHkXWaPvuNOt+99G75NrV0OS2EqHx5wMN7popYjpc8oTjC1y16DLg=="
+      },
+      "System.Text.Encodings.Web": {
+        "type": "Transitive",
+        "resolved": "8.0.0",
+        "contentHash": "yev/k9GHAEGx2Rg3/tU6MQh4HGBXJs70y7j1LaM1i/ER9po+6nnQ6RRqTJn1E7Xu0fbIFK80Nh5EoODxrbxwBQ==",
+        "dependencies": {
+          "System.Buffers": "4.5.1",
+          "System.Memory": "4.5.5",
+          "System.Runtime.CompilerServices.Unsafe": "6.0.0"
+        }
+      },
+      "System.Threading.Tasks.Extensions": {
+        "type": "Transitive",
+        "resolved": "4.5.4",
+        "contentHash": "zteT+G8xuGu6mS+mzDzYXbzS7rd3K6Fjb9RiZlYlJPam2/hU7JCBZBVEcywNuR+oZ1ncTvc/cq0faRr3P01OVg==",
+        "dependencies": {
+          "System.Runtime.CompilerServices.Unsafe": "4.5.3"
+        }
       }
     }
   }

test/NLogTarget.Tests/NLogTargetTests.cs

@@ -233,6 +233,88 @@
             Assert.AreEqual("Value", telemetry.Properties["Name"]);
         }
 
+        [TestMethod]
+        [TestCategory("NLogTarget")]
+        public void TraceHasComplexPropertiesSerializedAsJson()
+        {
+            var aiLogger = this.CreateTargetWithGivenConnectionString();
+
+            var complexObject = new
+            {
+                Name = "John Doe",
+                Age = 30,
+                Address = new
+                {
+                    Street = "123 Main St",
+                    City = "New York",
+                    ZipCode = "10001"
+                },
+                Tags = new[] { "tag1", "tag2", "tag3" }
+            };
+
+            var eventInfo = new LogEventInfo(LogLevel.Trace, "TestLogger", "Hello!");
+            eventInfo.Properties["ComplexObject"] = complexObject;
+            eventInfo.Properties["SimpleString"] = "SimpleValue";
+            aiLogger.Log(eventInfo);
+
+            var telemetry = this.adapterHelper.Channel.SentItems.FirstOrDefault() as TraceTelemetry;
+            Assert.IsNotNull(telemetry, "Didn't get the log event from the channel");
+
+            // Simple string should remain as is
+            Assert.AreEqual("SimpleValue", telemetry.Properties["SimpleString"]);
+
+            // Complex object should be serialized to JSON
+            Assert.IsTrue(telemetry.Properties.ContainsKey("ComplexObject"), "ComplexObject property not found");
+            var complexJson = telemetry.Properties["ComplexObject"];
+
+            // Verify it's JSON and contains expected properties
+            Assert.IsTrue(complexJson.Contains("\"Name\""), "JSON should contain Name property");
+            Assert.IsTrue(complexJson.Contains("\"John Doe\""), "JSON should contain Name value");
+            Assert.IsTrue(complexJson.Contains("\"Age\""), "JSON should contain Age property");
+            Assert.IsTrue(complexJson.Contains("30"), "JSON should contain Age value");
+            Assert.IsTrue(complexJson.Contains("\"Address\""), "JSON should contain Address property");
+            Assert.IsTrue(complexJson.Contains("\"Street\""), "JSON should contain nested Street property");
+            Assert.IsTrue(complexJson.Contains("\"123 Main St\""), "JSON should contain nested Street value");
+            Assert.IsTrue(complexJson.Contains("\"Tags\""), "JSON should contain Tags array");
+            Assert.IsTrue(complexJson.Contains("\"tag1\""), "JSON should contain array values");
+        }
+
+        [TestMethod]
+        [TestCategory("NLogTarget")]
+        public void TraceHandlesVariousPropertyTypes()
+        {
+            var aiLogger = this.CreateTargetWithGivenConnectionString();
+
+            var eventInfo = new LogEventInfo(LogLevel.Info, "TestLogger", "Testing various types");
+            eventInfo.Properties["String"] = "Simple string";
+            eventInfo.Properties["Int"] = 42;
+            eventInfo.Properties["Bool"] = true;
+            eventInfo.Properties["Decimal"] = 3.14m;
+            eventInfo.Properties["DateTime"] = new DateTime(2024, 1, 1, 12, 0, 0, DateTimeKind.Utc);
+            eventInfo.Properties["Array"] = new[] { 1, 2, 3 };
+            eventInfo.Properties["Dictionary"] = new Dictionary<string, object> { { "key1", "value1" }, { "key2", 123 } };
+            eventInfo.Properties["Null"] = null;
+
+            aiLogger.Log(eventInfo);
+
+            var telemetry = this.adapterHelper.Channel.SentItems.FirstOrDefault() as TraceTelemetry;
+            Assert.IsNotNull(telemetry, "Didn't get the log event from the channel");
+
+            // Simple types should be preserved as strings
+            Assert.AreEqual("Simple string", telemetry.Properties["String"]);
+            Assert.AreEqual("42", telemetry.Properties["Int"]);
+            Assert.AreEqual("True", telemetry.Properties["Bool"]);
+            Assert.IsTrue(telemetry.Properties["Decimal"].Contains("3.14"), "Decimal value should contain 3.14");
+
+            // Complex types should be serialized to JSON
+            Assert.IsTrue(telemetry.Properties["Array"].Contains("["), "Array should be JSON array");
+            Assert.IsTrue(telemetry.Properties["Array"].Contains("1"), "Array should contain values");
+            Assert.IsTrue(telemetry.Properties["Dictionary"].Contains("key1"), "Dictionary should be serialized");
+            Assert.IsTrue(telemetry.Properties["Dictionary"].Contains("value1"), "Dictionary should contain values");
+
+            // Null should be empty string
+            Assert.AreEqual(string.Empty, telemetry.Properties["Null"]);
+        }
 
         [TestMethod]
         [TestCategory("NLogTarget")]