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Handle nullable types in OpenAPI schemas and add corresponding unit t… #7170

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6c42ae8
fix: Handle nullable types in OpenAPI schemas and add corresponding u…
X39 Nov 28, 2025
89e9c09
fix: nullable enum support in OpenAPI schemas
X39 Nov 29, 2025
592710a
fix: support integer-based enums for C#.
X39 Nov 29, 2025
8de37c7
Add reverse test cases
X39 Jan 27, 2026
d1eed2d
Add GetSchemaReferenceIds test, covering nullable handling
X39 Jan 27, 2026
8833173
Merge upstream/main
X39 Mar 6, 2026
f82b3c6
Fix integer enum handling in union/intersection models
X39 Mar 6, 2026
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6 changes: 6 additions & 0 deletions src/Kiota.Builder/CodeDOM/CodeEnum.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using Microsoft.OpenApi;

namespace Kiota.Builder.CodeDOM;
#pragma warning disable CA1711
Expand Down Expand Up @@ -42,4 +43,9 @@ public CodeConstant? CodeEnumObject
{
get; set;
}

public JsonSchemaType? BackingType
{
get; set;
}
}
6 changes: 5 additions & 1 deletion src/Kiota.Builder/Extensions/OpenApiSchemaExtensions.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,8 @@ public static IEnumerable<string> GetSchemaNames(this IOpenApiSchema schema, boo
return schema switch
{
OpenApiSchemaReference reference => reference.Reference?.Id,
// Quickfix for https://github.com/microsoft/kiota/issues/6776 ToDo: Properly handle nullable types in accordance with OpenAPI 3.
OpenApiSchema {OneOf: [OpenApiSchema{Type: JsonSchemaType.Null}, OpenApiSchemaReference reference]} => reference.Reference?.Id,
OpenApiSchema s when s.GetMergedSchemaOriginalReferenceId() is string originalReferenceId => originalReferenceId,
_ => null,
};
Expand All @@ -59,6 +61,8 @@ public static bool IsReferencedSchema(this IOpenApiSchema schema)
return schema switch
{
OpenApiSchemaReference => true,
// Quickfix for https://github.com/microsoft/kiota/issues/6776 ToDo: Properly handle nullable types in accordance with OpenAPI 3.
OpenApiSchema {OneOf: [OpenApiSchema{Type: JsonSchemaType.Null}, OpenApiSchemaReference reference]} => true,
_ => false,
};
}
Expand Down Expand Up @@ -318,7 +322,7 @@ public static bool IsSemanticallyMeaningful(this IOpenApiSchema schema, bool ign
return schema.HasAnyProperty() ||
(!ignoreEnums && schema.Enum is { Count: > 0 }) ||
(!ignoreArrays && schema.Items != null) ||
(!ignoreType && schema.Type is not null &&
(!ignoreType && schema.Type is not null and not JsonSchemaType.Null &&
((ignoreNullableObjects && !schema.IsObjectType()) ||
!ignoreNullableObjects)) ||
!string.IsNullOrEmpty(schema.Format) ||
Expand Down
1 change: 1 addition & 0 deletions src/Kiota.Builder/KiotaBuilder.cs
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Expand Up @@ -2021,6 +2021,7 @@ private CodeElement AddModelDeclarationIfDoesntExist(OpenApiUrlTreeNode currentN
currentNode.GetPathItemDescription(Constants.DefaultOpenApiLabel),
},
Deprecation = schema.GetDeprecationInformation(),
BackingType = schema.Type,
};
SetEnumOptions(schema, newEnum);
return currentNamespace.AddEnum(newEnum).First();
Expand Down
73 changes: 62 additions & 11 deletions src/Kiota.Builder/Writers/CSharp/CodeMethodWriter.cs
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Expand Up @@ -4,6 +4,7 @@
using Kiota.Builder.CodeDOM;
using Kiota.Builder.Extensions;
using Kiota.Builder.OrderComparers;
using Microsoft.OpenApi;

namespace Kiota.Builder.Writers.CSharp;

Expand Down Expand Up @@ -141,10 +142,21 @@ private void WriteFactoryMethodBodyForUnionModel(CodeMethod codeElement, CodeCla
}
else if (propertyType.TypeDefinition is CodeClass && propertyType.IsCollection || propertyType.TypeDefinition is null || propertyType.TypeDefinition is CodeEnum)
{
var readerReference = parseNodeParameter.Name.ToFirstCharacterLowerCase();
var selfReference = $"{ResultVarName}.{property.Name.ToFirstCharacterUpperCase()}";
var deserializationMethodName = GetDeserializationMethodName(propertyType, codeElement);
var typeName = conventions.GetTypeString(propertyType, codeElement, true, (propertyType.TypeDefinition is CodeEnum || conventions.IsPrimitiveType(propertyType.Name)) && propertyType.CollectionKind is not CodeTypeBase.CodeTypeCollectionKind.None);
var valueVarName = $"{property.Name.ToFirstCharacterLowerCase()}Value";
writer.WriteLine($"{(includeElse ? "else " : string.Empty)}if({parseNodeParameter.Name.ToFirstCharacterLowerCase()}.{GetDeserializationMethodName(propertyType, codeElement)} is {typeName} {valueVarName})");
writer.WriteBlock(lines: $"{ResultVarName}.{property.Name.ToFirstCharacterUpperCase()} = {valueVarName};");
if (propertyType.TypeDefinition is CodeType { TypeDefinition: CodeEnum {BackingType: JsonSchemaType.Integer}})
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@gavinbarron gavinbarron Jan 23, 2026

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This need test coverage to ensure the deserialization code is generated correctly for the case of a union model with an integer enum.

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@X39 X39 Jan 27, 2026

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I am not entirely sure what you mean by that, could you provide a sample json?
Also, where are those tests currently located at?

Thanks in advance

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@gavinbarron gavinbarron Jan 28, 2026

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Here's where the tests for this method start:

kiota/tests/Kiota.Builder.Tests/Writers/CSharp/CodeMethodWriterTests.cs

Line 592 in 2848c0b

public void WritesModelFactoryBodyForUnionModels()

A union model with and integer enum might looks something like:

openapi: 3.0.3
info:
  title: Union with Integer Enum API
  version: 1.0.0
servers:
  - url: https://api.example.com/v1

paths:
  /status:
    get:
      summary: Get status that can be multiple types
      responses:
        '200':
          description: A union type containing an integer enum
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/StatusUnion'

components:
  schemas:
    # Integer-backed enum
    StatusEnum:
      type: integer
      enum: [0, 1, 2]
      x-ms-enum:
        name: StatusEnum
        modelAsString: false
        values:
          - name: Active
            value: 0
            description: "The resource is active"
          - name: Inactive
            value: 1
            description: "The resource is inactive"
          - name: Pending
            value: 2
            description: "The resource is pending"
    
    # A complex object type
    DetailedStatus:
      type: object
      required:
        - message
      properties:
        message:
          type: string
        code:
          type: integer
    
    # Union model combining integer enum and object
    StatusUnion:
      oneOf:
        - $ref: '#/components/schemas/StatusEnum'
        - $ref: '#/components/schemas/DetailedStatus'
      discriminator:
        propertyName: '@odata.type'
        mapping:
          '#kiota.statusEnum': '#/components/schemas/StatusEnum'
          '#kiota.detailedStatus': '#/components/schemas/DetailedStatus'

{
writer.WriteLine($"{(includeElse ? "else " : string.Empty)}if({readerReference}.{deserializationMethodName} is int {valueVarName})");
writer.WriteBlock(lines: $"{selfReference} = ({typeName}){valueVarName};");
}
else
{
writer.WriteLine($"{(includeElse ? "else " : string.Empty)}if({readerReference}.{deserializationMethodName} is {typeName} {valueVarName})");
writer.WriteBlock(lines: $"{selfReference} = {valueVarName};");
}
}
if (!includeElse)
includeElse = true;
Expand All @@ -162,10 +174,21 @@ private void WriteFactoryMethodBodyForIntersectionModel(CodeMethod codeElement,
{
if (property.Type is CodeType propertyType)
{
var readerReference = parseNodeParameter.Name.ToFirstCharacterLowerCase();
var selfReference = $"{ResultVarName}.{property.Name.ToFirstCharacterUpperCase()}";
var deserializationMethodName = GetDeserializationMethodName(propertyType, codeElement);
var typeName = conventions.GetTypeString(propertyType, codeElement, true, propertyType.TypeDefinition is CodeEnum && propertyType.CollectionKind is not CodeTypeBase.CodeTypeCollectionKind.None);
var valueVarName = $"{property.Name.ToFirstCharacterLowerCase()}Value";
writer.WriteLine($"{(includeElse ? "else " : string.Empty)}if({parseNodeParameter.Name.ToFirstCharacterLowerCase()}.{GetDeserializationMethodName(propertyType, codeElement)} is {typeName} {valueVarName})");
writer.WriteBlock(lines: $"{ResultVarName}.{property.Name.ToFirstCharacterUpperCase()} = {valueVarName};");
if (propertyType.TypeDefinition is CodeType { TypeDefinition: CodeEnum {BackingType: JsonSchemaType.Integer}})
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This need test coverage to ensure the deserialization code is generated correctly for the case of a intersection model with an integer enum.

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@X39 X39 Jan 27, 2026

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I am not entirely sure what you mean by that, could you provide a sample json?
Also, where are those tests currently located at?

Thanks in advance

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Intersection model tests start here:

kiota/tests/Kiota.Builder.Tests/Writers/CSharp/CodeMethodWriterTests.cs

Line 891 in 2848c0b

public void WritesModelFactoryBodyForIntersectionModels()

Example of an intersection model based on the previous union model example

    StatusIntersection:
      allOf:
        - $ref: '#/components/schemas/StatusEnum'
        - $ref: '#/components/schemas/DetailedStatus'

{
writer.WriteLine($"{(includeElse ? "else " : string.Empty)}if({readerReference}.{deserializationMethodName} is int {valueVarName})");
writer.WriteBlock(lines: $"{selfReference} = ({typeName}){valueVarName};");
}
else
{
writer.WriteLine($"{(includeElse ? "else " : string.Empty)}if({readerReference}.{deserializationMethodName} is {typeName} {valueVarName})");
writer.WriteBlock(lines: $"{selfReference} = {valueVarName};");
}
}
if (!includeElse)
includeElse = true;
Expand Down Expand Up @@ -349,7 +372,13 @@ private void WriteDeserializerBodyForInheritedModel(bool shouldHide, CodeMethod
.Where(static x => !x.ExistsInBaseType)
.OrderBy(static x => x.Name, StringComparer.Ordinal))
{
writer.WriteLine($"{{ \"{otherProp.WireName}\", n => {{ {otherProp.Name.ToFirstCharacterUpperCase()} = n.{GetDeserializationMethodName(otherProp.Type, codeElement)}; }} }},");
if (otherProp is {Type: CodeType { TypeDefinition: CodeEnum {BackingType: JsonSchemaType.Integer}} propertyType})
{
var typeName = conventions.GetTypeString(propertyType, codeElement, true, (propertyType.TypeDefinition is CodeEnum || conventions.IsPrimitiveType(propertyType.Name)) && propertyType.CollectionKind is not CodeTypeBase.CodeTypeCollectionKind.None);
writer.WriteLine($"{{ \"{otherProp.WireName}\", n => {{ {otherProp.Name.ToFirstCharacterUpperCase()} = ({typeName}?) n.{GetDeserializationMethodName(otherProp.Type, codeElement)}; }} }},");
}
else
writer.WriteLine($"{{ \"{otherProp.WireName}\", n => {{ {otherProp.Name.ToFirstCharacterUpperCase()} = n.{GetDeserializationMethodName(otherProp.Type, codeElement)}; }} }},");
}
writer.CloseBlock("};");
}
Expand All @@ -370,7 +399,10 @@ private string GetDeserializationMethodName(CodeTypeBase propType, CodeMethod me
return $"GetCollectionOfObjectValues<{propertyType}>({propertyType}.CreateFromDiscriminatorValue){collectionMethod}";
}
else if (currentType.TypeDefinition is CodeEnum enumType)
return $"GetEnumValue<{enumType.GetFullName()}>()";
if (enumType.BackingType is JsonSchemaType.Integer)
return $"GetIntValue()";
else
return $"GetEnumValue<{enumType.GetFullName()}>()";
}
return propertyType switch
{
Expand Down Expand Up @@ -482,7 +514,10 @@ private void WriteSerializerBodyForInheritedModel(bool shouldHide, CodeMethod me
.OrderBy(static x => x.Name))
{
var serializationMethodName = GetSerializationMethodName(otherProp.Type, method);
writer.WriteLine($"writer.{serializationMethodName}(\"{otherProp.WireName}\", {otherProp.Name.ToFirstCharacterUpperCase()});");
if (otherProp.Type is CodeType{TypeDefinition: CodeEnum {BackingType: JsonSchemaType.Integer}})
writer.WriteLine($"writer.{serializationMethodName}(\"{otherProp.WireName}\", (int?){otherProp.Name.ToFirstCharacterUpperCase()});");
else
writer.WriteLine($"writer.{serializationMethodName}(\"{otherProp.WireName}\", {otherProp.Name.ToFirstCharacterUpperCase()});");
}
}
private void WriteSerializerBodyForUnionModel(CodeMethod method, CodeClass parentClass, LanguageWriter writer)
Expand All @@ -494,8 +529,12 @@ private void WriteSerializerBodyForUnionModel(CodeMethod method, CodeClass paren
.OrderBy(static x => x, CodePropertyTypeForwardComparer)
.ThenBy(static x => x.Name))
{
var serializationMethodName = GetSerializationMethodName(otherProp.Type, method);
writer.WriteLine($"{(includeElse ? "else " : string.Empty)}if({otherProp.Name.ToFirstCharacterUpperCase()} != null)");
writer.WriteBlock(lines: $"writer.{GetSerializationMethodName(otherProp.Type, method)}(null, {otherProp.Name.ToFirstCharacterUpperCase()});");
if (otherProp.Type is CodeType{TypeDefinition: CodeEnum {BackingType: JsonSchemaType.Integer}})
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I'm not seeing any tests for serialization of union models that include Integer Enums, let's make sure test cases for this are added.

It feels a bit weird that the integer case is passing otherProp.WireName which is inconsistent with how the existing case works.

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@X39 X39 Jan 27, 2026

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I am very aware of that, wanted to avoid cross-repository changes tho and have this easily integrateable on my end.

Could you hint me at where those tests are currently placed and how they look? Thanks in advance.

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@gavinbarron gavinbarron Jan 28, 2026

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Here's where we have an existing test for the union model serialization

kiota/tests/Kiota.Builder.Tests/Writers/CSharp/CodeMethodWriterTests.cs

Line 1394 in 2848c0b

public void WritesUnionDeSerializerBody()

It focuses on the code that is generated, rather than the behavior of the serialization library that we have as a dependency.

writer.WriteBlock(lines: $"writer.{serializationMethodName}(\"{otherProp.WireName}\", (int?){otherProp.Name.ToFirstCharacterUpperCase()});");
else
writer.WriteBlock(lines: $"writer.{serializationMethodName}(null, {otherProp.Name.ToFirstCharacterUpperCase()});");
if (!includeElse)
includeElse = true;
}
Expand All @@ -510,8 +549,12 @@ private void WriteSerializerBodyForIntersectionModel(CodeMethod method, CodeClas
.OrderBy(static x => x, CodePropertyTypeBackwardComparer)
.ThenBy(static x => x.Name))
{
var serializationMethodName = GetSerializationMethodName(otherProp.Type, method);
writer.WriteLine($"{(includeElse ? "else " : string.Empty)}if({otherProp.Name.ToFirstCharacterUpperCase()} != null)");
writer.WriteBlock(lines: $"writer.{GetSerializationMethodName(otherProp.Type, method)}(null, {otherProp.Name.ToFirstCharacterUpperCase()});");
if (otherProp.Type is CodeType{TypeDefinition: CodeEnum {BackingType: JsonSchemaType.Integer}})
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@gavinbarron gavinbarron Jan 23, 2026

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I'm not seeing any tests for serialization of intersection models that include Integer Enums, let's make sure test cases for this are added.

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@X39 X39 Jan 27, 2026

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I am not entirely sure what you mean by that, could you provide a sample json?
Also, where are those tests currently located at?

Thanks in advance

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Here's the existing test for generating the serialization method

kiota/tests/Kiota.Builder.Tests/Writers/CSharp/CodeMethodWriterTests.cs

Line 1419 in 2848c0b

public void WritesIntersectionDeSerializerBody()

I have supplied sample open api for these types of schema on the factory method/deserialization comments

writer.WriteBlock(lines: $"writer.{serializationMethodName}(\"{otherProp.WireName}\", (int?){otherProp.Name.ToFirstCharacterUpperCase()});");
else
writer.WriteBlock(lines: $"writer.{serializationMethodName}(null, {otherProp.Name.ToFirstCharacterUpperCase()});");
if (!includeElse)
includeElse = true;
}
Expand All @@ -529,7 +572,12 @@ private void WriteSerializerBodyForIntersectionModel(CodeMethod method, CodeClas
.Select(static x => x.Name.ToFirstCharacterUpperCase())
.OrderBy(static x => x)
.Aggregate(static (x, y) => $"{x}, {y}");
writer.WriteLine($"writer.{GetSerializationMethodName(complexProperties.First().Type, method)}(null, {propertiesNames});");
var prop = complexProperties.First();
var serializationMethodName = GetSerializationMethodName(prop.Type, method);
if (prop.Type is CodeType{TypeDefinition: CodeEnum {BackingType: JsonSchemaType.Integer}})
writer.WriteLine($"writer.{serializationMethodName}(\"{prop.WireName}\", (int?){prop.Name.ToFirstCharacterUpperCase()});");
else
writer.WriteLine($"writer.{GetSerializationMethodName(complexProperties.First().Type, method)}(null, {propertiesNames});");
if (includeElse)
{
writer.CloseBlock();
Expand Down Expand Up @@ -678,7 +726,10 @@ private string GetSerializationMethodName(CodeTypeBase propType, CodeMethod meth
else
return $"WriteCollectionOfObjectValues<{propertyType}>";
else if (currentType.TypeDefinition is CodeEnum enumType)
return $"WriteEnumValue<{enumType.GetFullName()}>";
if (enumType.BackingType is JsonSchemaType.Integer)
return $"WriteIntValue";
else
return $"WriteEnumValue<{enumType.GetFullName()}>";

}
return propertyType switch
Expand Down
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