Fix/6836 query parameters default value

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Fixes a bug where invalid C# code is generated when API path contains an underscore [#6698](https://github.com/microsoft/kiota/issues/6698)
 - Fixed a bug where union of integer and boolean types collection would not compile in dotnet. [#6834](https://github.com/microsoft/kiota/issues/6834)
+- Fixed a bug where default values for query parameters are not generated in C# code. [#6836](https://github.com/microsoft/kiota/issues/6836)
 
 ## [1.28.0] - 2025-07-11
 

src/Kiota.Builder/KiotaBuilder.cs

@@ -1201,12 +1201,21 @@ openApiExtension is OpenApiPrimaryErrorMessageExtension primaryErrorMessageExten
         if (prop.IsOfKind(CodePropertyKind.Custom, CodePropertyKind.QueryParameter) &&
             !propertyName.Equals(childIdentifier, StringComparison.Ordinal))
             prop.SerializationName = childIdentifier;
-        if (kind == CodePropertyKind.Custom &&
-            propertySchema?.Default is JsonValue stringDefaultJsonValue &&
-            stringDefaultJsonValue.TryGetValue<string>(out var stringDefaultValue) &&
-            !string.IsNullOrEmpty(stringDefaultValue) &&
-            !"null".Equals(stringDefaultValue, StringComparison.OrdinalIgnoreCase))
-            prop.DefaultValue = $"\"{stringDefaultValue}\"";
+        if ((kind == CodePropertyKind.Custom || kind == CodePropertyKind.QueryParameter) &&
+        propertySchema?.Default is JsonValue defaultJsonValue &&
+        defaultJsonValue.TryGetValue<string>(out var stringDefaultValue) &&
+        !string.IsNullOrEmpty(stringDefaultValue) &&
+        !"null".Equals(stringDefaultValue, StringComparison.OrdinalIgnoreCase))
+        {
+            if (propertySchema.Type == JsonSchemaType.Integer && int.TryParse(stringDefaultValue, out var intValue))
+                prop.DefaultValue = intValue.ToString(CultureInfo.InvariantCulture);
+            else if (propertySchema.Type == JsonSchemaType.Number && double.TryParse(stringDefaultValue, out var doubleValue))
+                prop.DefaultValue = doubleValue.ToString(CultureInfo.InvariantCulture);
+            else if (propertySchema.Type == JsonSchemaType.Boolean && bool.TryParse(stringDefaultValue, out var boolValue))
+                prop.DefaultValue = boolValue.ToString().ToLowerInvariant();
+            else
+                prop.DefaultValue = $"\"{stringDefaultValue}\"";
+        }
 
         if (existingType == null)
         {

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

@@ -38,6 +38,19 @@ private void WritePropertyInternal(CodeProperty codeElement, LanguageWriter writ
         var setterAccessModifier = codeElement.ReadOnly && codeElement.Access > AccessModifier.Private ? "private " : string.Empty;
         var simpleBody = $"get; {setterAccessModifier}set;";
         var defaultValue = string.Empty;
+        if (!string.IsNullOrEmpty(codeElement.DefaultValue))
+        {
+            if (codeElement.Type is CodeType propertyCodeType && propertyCodeType.TypeDefinition is CodeEnum enumDefinition)
+            {
+                var enumTypeName = conventions.GetTypeString(codeElement.Type, codeElement).TrimEnd('?');
+                var enumValue = codeElement.DefaultValue.Trim('"').CleanupSymbolName().ToFirstCharacterUpperCase();
+                defaultValue = $" = {enumTypeName}.{enumValue};";
+            }
+            else
+            {
+                defaultValue = $" = {codeElement.DefaultValue};";
+            }
+        }
         switch (codeElement.Kind)
         {
             case CodePropertyKind.RequestBuilder:

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

@@ -88,6 +88,99 @@ public void WritesCustomProperty()
         Assert.Contains("get; set;", result);
     }
     [Fact]
+    public void WritesCustomPropertyWithDefaultValue()
+    {
+        property.Kind = CodePropertyKind.Custom;
+        property.DefaultValue = $"new {TypeName}()";
+        writer.Write(property);
+        var result = tw.ToString();
+        Assert.Contains($"{TypeName} {PropertyName}", result);
+        Assert.Contains("get; set;", result);
+        Assert.Contains($" = new {TypeName}()", result);
+    }
+    [Fact]
+    public void WritesQueryParameterWithDefaultEnumValue()
+    {
+        var enumProperty = new CodeProperty
+        {
+            Name = "EnumProperty",
+            Type = new CodeType
+            {
+                Name = "SomeEnum",
+                TypeDefinition = rootNamespace.AddEnum(new CodeEnum
+                {
+                    Name = "SomeEnum"
+                }).First()
+            },
+            Kind = CodePropertyKind.QueryParameter,
+            DefaultValue = "EnumValue2",
+        };
+        parentClass.AddProperty(enumProperty, new()
+        {
+            Name = "queryParameter",
+            Kind = CodePropertyKind.QueryParameter,
+            Type = new CodeType
+            {
+                Name = "QueryParameter",
+            },
+        });
+        writer.Write(enumProperty);
+        var result = tw.ToString();
+        Assert.Contains("SomeEnum? EnumProperty { get; set; } = global::defaultNamespace.SomeEnum.EnumValue2;", result);
+    }
+    [Fact]
+    public void WritesQueryParameterWithDefaultIntValue()
+    {
+        var integerProperty = new CodeProperty
+        {
+            Name = "IntegerProperty",
+            Type = new CodeType
+            {
+                Name = "Int32"
+            },
+            Kind = CodePropertyKind.QueryParameter,
+            DefaultValue = "3",
+        };
+        parentClass.AddProperty(integerProperty, new()
+        {
+            Name = "queryParameter",
+            Kind = CodePropertyKind.QueryParameter,
+            Type = new CodeType
+            {
+                Name = "QueryParameter",
+            },
+        });
+        writer.Write(integerProperty);
+        var result = tw.ToString();
+        Assert.Contains("Int32? IntegerProperty { get; set; } = 3;", result);
+    }
+    [Fact]
+    public void WritesQueryParameterWithDefaultStringValue()
+    {
+        var stringProperty = new CodeProperty
+        {
+            Name = "StringProperty",
+            Type = new CodeType
+            {
+                Name = "String"
+            },
+            Kind = CodePropertyKind.QueryParameter,
+            DefaultValue = "\"SomeString\"",
+        };
+        parentClass.AddProperty(stringProperty, new()
+        {
+            Name = "queryParameter",
+            Kind = CodePropertyKind.QueryParameter,
+            Type = new CodeType
+            {
+                Name = "QueryParameter",
+            },
+        });
+        writer.Write(stringProperty);
+        var result = tw.ToString();
+        Assert.Contains("public String? StringProperty { get; set; } = \"SomeString\";", result);
+    }
+    [Fact]
     public void WritesPrivateSetter()
     {
         property.Kind = CodePropertyKind.Custom;