Override ApiException.Message getter to include ResponseStatusCode

src/Kiota.Builder/Writers/CSharp/CodePropertyWriter.cs

@@ -62,7 +62,7 @@ private void WritePropertyInternal(CodeProperty codeElement, LanguageWriter writ
                 if (parentClass.GetPrimaryMessageCodePath(static x => x.Name.ToFirstCharacterUpperCase(), static x => x.Name.ToFirstCharacterUpperCase(), "?.") is string primaryMessageCodePath && !string.IsNullOrEmpty(primaryMessageCodePath))
                     writer.WriteLine($"public override {propertyType} {codeElement.Name.ToFirstCharacterUpperCase()} {{ get => {primaryMessageCodePath} ?? string.Empty; }}");
                 else
-                    writer.WriteLine($"public override {propertyType} {codeElement.Name.ToFirstCharacterUpperCase()} {{ get => base.Message; }}");
+                    writer.WriteLine($"public override {propertyType} {codeElement.Name.ToFirstCharacterUpperCase()} {{ get => $\"{{ResponseStatusCode}}: {{base.Message}}\"; }}");
                 break;
             case CodePropertyKind.QueryParameter when codeElement.IsNameEscaped:
                 writer.WriteLine($"[QueryParameter(\"{codeElement.SerializationName}\")]");

tests/Kiota.Builder.Tests/Writers/CSharp/CodePropertyWriterTests.cs

@@ -249,5 +249,29 @@ public void WritesMessageOverrideOnPrimary()
         // Then
         Assert.Contains("public override string Message { get => Prop1 ?? string.Empty; }", result);
     }
+
+    [Fact]
+    public void WritesMessageOverrideWithStatusCodeWhenNoPrimaryMessage()
+    {
+        // Given
+        parentClass.IsErrorDefinition = true;
+        // No primary error message property added
+        var overrideProperty = parentClass.AddProperty(new CodeProperty
+        {
+            Name = "Message",
+            Kind = CodePropertyKind.ErrorMessageOverride,
+            Type = new CodeType
+            {
+                Name = "string",
+            },
+        }).First();
+
+        // When
+        writer.Write(overrideProperty);
+        var result = tw.ToString();
+
+        // Then
+        Assert.Contains("public override string Message { get => $\"{ResponseStatusCode}: {base.Message}\"; }", result);
+    }
 }