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Fix: Base type not generated for types using oneOf with discriminator #906

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Merged
christianhelle merged 4 commits into from
Mar 4, 2026
Merged

Fix: Base type not generated for types using oneOf with discriminator #906

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85af425
Initial plan
Copilot Feb 20, 2026
edaf6b6
Initial exploration - understanding oneOf with discriminator issue
Copilot Feb 20, 2026
7cd060f
Fix: Base type not generated for types specified by oneOf in the schema
Copilot Feb 20, 2026
81ef306
Add anyOf with discriminator test cases
Copilot Mar 4, 2026
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43 changes: 43 additions & 0 deletions src/Refitter.Core/CSharpClientGeneratorFactory.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@ public CustomCSharpClientGenerator Create()
}
}

ConvertOneOfWithDiscriminatorToAllOf();
FixMissingTypesWithIntegerFormat();
ApplyCustomIntegerType();

Expand Down Expand Up @@ -65,6 +66,48 @@ public CustomCSharpClientGenerator Create()
return generator;
}

/// <summary>
/// Converts schemas that use oneOf/anyOf with a discriminator to use the allOf inheritance
/// pattern that NSwag's C# code generator understands. Without this transformation,
/// NSwag generates undefined anonymous types (e.g., "IdentityProvider2") instead of
/// proper base class references.
/// </summary>
private void ConvertOneOfWithDiscriminatorToAllOf()
{
foreach (var kvp in document.Components.Schemas)
{
var schema = kvp.Value.ActualSchema;

if (schema.DiscriminatorObject == null)
continue;

var unionSchemas = schema.OneOf.Concat(schema.AnyOf).ToArray();
if (unionSchemas.Length == 0)
continue;

// Ensure the base schema is typed as an object
if (schema.Type == JsonObjectType.None || schema.Type == JsonObjectType.Null)
schema.Type = JsonObjectType.Object;

// For each subtype, add allOf pointing to the base schema if not already present
foreach (var subSchemaRef in unionSchemas)
{
var subSchema = subSchemaRef.ActualSchema;
bool alreadyInherits = subSchema.AllOf.Any(
a => a.HasReference && a.ActualSchema == schema);
if (!alreadyInherits)
{
var reference = new JsonSchema { Reference = schema };
subSchema.AllOf.Add(reference);
}
}

// Remove the oneOf/anyOf from the base schema now that subtypes use allOf
schema.OneOf.Clear();
schema.AnyOf.Clear();
}
}

private void FixMissingTypesWithIntegerFormat()
{
ProcessSchemasForMissingTypes(document.Components.Schemas);
Expand Down
283 changes: 283 additions & 0 deletions src/Refitter.Tests/Examples/OneOfDiscriminatorTests.cs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,283 @@
using FluentAssertions;
using Refitter.Core;
using Refitter.Tests.Build;
using Refitter.Tests.TestUtilities;
using TUnit.Core;

namespace Refitter.Tests.Examples;

public class OneOfDiscriminatorTests
{
private const string OpenApiSpec = @"
openapi: 3.0.1
info:
title: Test
version: v1
paths:
/api/identityproviders:
get:
operationId: GetIdentityProvider
responses:
'200':
description: Success
content:
application/json:
schema:
$ref: '#/components/schemas/IdentityProviderResponse'
components:
schemas:
IdentityProviderResponse:
type: object
properties:
identityProvider:
$ref: '#/components/schemas/IdentityProvider'
identityProviders:
type: array
items:
$ref: '#/components/schemas/IdentityProvider'
IdentityProvider:
oneOf:
- $ref: '#/components/schemas/AppleIdentityProvider'
- $ref: '#/components/schemas/FacebookIdentityProvider'
discriminator:
propertyName: type
mapping:
Apple: '#/components/schemas/AppleIdentityProvider'
Facebook: '#/components/schemas/FacebookIdentityProvider'
AppleIdentityProvider:
type: object
properties:
type:
type: string
bundleId:
type: string
FacebookIdentityProvider:
type: object
properties:
type:
type: string
appId:
type: string
";

private const string AnyOfOpenApiSpec = @"
openapi: 3.0.1
info:
title: Test
version: v1
paths:
/api/notifications:
get:
operationId: GetNotification
responses:
'200':
description: Success
content:
application/json:
schema:
$ref: '#/components/schemas/NotificationResponse'
components:
schemas:
NotificationResponse:
type: object
properties:
notification:
$ref: '#/components/schemas/Notification'
notifications:
type: array
items:
$ref: '#/components/schemas/Notification'
Notification:
anyOf:
- $ref: '#/components/schemas/EmailNotification'
- $ref: '#/components/schemas/SmsNotification'
discriminator:
propertyName: channel
mapping:
Email: '#/components/schemas/EmailNotification'
Sms: '#/components/schemas/SmsNotification'
EmailNotification:
type: object
properties:
channel:
type: string
emailAddress:
type: string
SmsNotification:
type: object
properties:
channel:
type: string
phoneNumber:
type: string
";

[Test]

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The ConvertOneOfWithDiscriminatorToAllOf method handles anyOf + discriminator (line 84 concatenates schema.AnyOf), but there is no test case for the anyOf with discriminator pattern. Given the test suite has comprehensive tests for oneOf + discriminator, the analogous anyOf path in the implementation is untested. If NSwag handles anyOf differently from oneOf during code generation, this path could silently produce incorrect output.

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public async Task Can_Generate_Code()
{
string generatedCode = await GenerateCode();
generatedCode.Should().NotBeNullOrWhiteSpace();
}

[Test]
public async Task Generates_Base_Type_For_OneOf_With_Discriminator()
{
string generatedCode = await GenerateCode();
generatedCode.Should().Contain("class IdentityProvider");

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The assertion generatedCode.Should().Contain("class IdentityProvider") at line 126 is a weak test because it can match class IdentityProviderResponse (which is always generated regardless of the fix). If only IdentityProviderResponse were present and IdentityProvider were missing, this test would still pass. A more precise assertion would use "class IdentityProvider\r", "class IdentityProvider\n", or a pattern that does not match the Response suffix, such as "\npartial class IdentityProvider" or a whitespace-terminated check. The same issue applies to line 207 ("class Notification") which could match the class NotificationResponse.

Suggested change
generatedCode.Should().Contain("class IdentityProvider");
generatedCode.Should().Contain("class IdentityProvider ");

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}

[Test]
public async Task Does_Not_Generate_Anonymous_Type_For_OneOf_With_Discriminator()
{
string generatedCode = await GenerateCode();
generatedCode.Should().NotContain("IdentityProvider2");
}

[Test]
public async Task Generates_All_Subtypes_For_OneOf_With_Discriminator()
{
string generatedCode = await GenerateCode();
generatedCode.Should().Contain("class AppleIdentityProvider");
generatedCode.Should().Contain("class FacebookIdentityProvider");
}

[Test]
public async Task Generates_Inheritance_Hierarchy_For_OneOf_With_Discriminator()
{
string generatedCode = await GenerateCode();
generatedCode.Should().Contain("AppleIdentityProvider : IdentityProvider");
generatedCode.Should().Contain("FacebookIdentityProvider : IdentityProvider");
}

[Test]
public async Task Generates_Correct_Property_Type_For_OneOf_With_Discriminator()
{
string generatedCode = await GenerateCode();
generatedCode.Should().Contain("IdentityProvider IdentityProvider");
generatedCode.Should().Contain("ICollection<IdentityProvider> IdentityProviders");
}

[Test]
public async Task Can_Build_Generated_Code()
{
string generatedCode = await GenerateCode();
BuildHelper
.BuildCSharp(generatedCode)
.Should()
.BeTrue();
}

[Test]
public async Task Can_Generate_Code_With_Polymorphic_Serialization()
{
string generatedCode = await GenerateCode(usePolymorphicSerialization: true);
generatedCode.Should().NotBeNullOrWhiteSpace();
}

[Test]
public async Task Generates_JsonPolymorphic_Attributes_For_OneOf_With_Discriminator()
{
string generatedCode = await GenerateCode(usePolymorphicSerialization: true);
generatedCode.Should().Contain("[JsonPolymorphic(TypeDiscriminatorPropertyName = \"type\"");
generatedCode.Should().Contain("[JsonDerivedType(typeof(AppleIdentityProvider)");
generatedCode.Should().Contain("[JsonDerivedType(typeof(FacebookIdentityProvider)");
}

[Test]
public async Task Can_Build_Generated_Code_With_Polymorphic_Serialization()
{
string generatedCode = await GenerateCode(usePolymorphicSerialization: true);
BuildHelper
.BuildCSharp(generatedCode)
.Should()
.BeTrue();
}

[Test]
public async Task Can_Generate_Code_For_AnyOf_With_Discriminator()
{
string generatedCode = await GenerateCode(spec: AnyOfOpenApiSpec);
generatedCode.Should().NotBeNullOrWhiteSpace();
}

[Test]
public async Task Generates_Base_Type_For_AnyOf_With_Discriminator()
{
string generatedCode = await GenerateCode(spec: AnyOfOpenApiSpec);
generatedCode.Should().Contain("class Notification");

Copilot AI Mar 4, 2026

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The assertion generatedCode.Should().Contain("class Notification") at line 207 is a weak test because it will also match class NotificationResponse (which is always generated). A more precise assertion should distinguish the base type Notification from the response wrapper, e.g. checking for "class Notification\n" or a partial class declaration pattern.

Suggested change
generatedCode.Should().Contain("class Notification");
generatedCode.Should().Contain("class Notification\n");

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}

[Test]
public async Task Does_Not_Generate_Anonymous_Type_For_AnyOf_With_Discriminator()
{
string generatedCode = await GenerateCode(spec: AnyOfOpenApiSpec);
generatedCode.Should().NotContain("Notification2");
}

[Test]
public async Task Generates_All_Subtypes_For_AnyOf_With_Discriminator()
{
string generatedCode = await GenerateCode(spec: AnyOfOpenApiSpec);
generatedCode.Should().Contain("class EmailNotification");
generatedCode.Should().Contain("class SmsNotification");
}

[Test]
public async Task Generates_Inheritance_Hierarchy_For_AnyOf_With_Discriminator()
{
string generatedCode = await GenerateCode(spec: AnyOfOpenApiSpec);
generatedCode.Should().Contain("EmailNotification : Notification");
generatedCode.Should().Contain("SmsNotification : Notification");
}

[Test]
public async Task Generates_Correct_Property_Type_For_AnyOf_With_Discriminator()
{
string generatedCode = await GenerateCode(spec: AnyOfOpenApiSpec);
generatedCode.Should().Contain("Notification Notification");
generatedCode.Should().Contain("ICollection<Notification> Notifications");
}

[Test]
public async Task Can_Build_Generated_Code_For_AnyOf_With_Discriminator()
{
string generatedCode = await GenerateCode(spec: AnyOfOpenApiSpec);
BuildHelper
.BuildCSharp(generatedCode)
.Should()
.BeTrue();
}

[Test]
public async Task Generates_JsonPolymorphic_Attributes_For_AnyOf_With_Discriminator()
{
string generatedCode = await GenerateCode(spec: AnyOfOpenApiSpec, usePolymorphicSerialization: true);
generatedCode.Should().Contain("[JsonPolymorphic(TypeDiscriminatorPropertyName = \"channel\"");
generatedCode.Should().Contain("[JsonDerivedType(typeof(EmailNotification)");
generatedCode.Should().Contain("[JsonDerivedType(typeof(SmsNotification)");
}

[Test]
public async Task Can_Build_Generated_Code_For_AnyOf_With_Discriminator_And_Polymorphic_Serialization()
{
string generatedCode = await GenerateCode(spec: AnyOfOpenApiSpec, usePolymorphicSerialization: true);
BuildHelper
.BuildCSharp(generatedCode)
.Should()
.BeTrue();
}

private static async Task<string> GenerateCode(string spec = OpenApiSpec, bool usePolymorphicSerialization = false)
{
var swaggerFile = await SwaggerFileHelper.CreateSwaggerFile(spec);
var settings = new RefitGeneratorSettings
{
OpenApiPath = swaggerFile,
UsePolymorphicSerialization = usePolymorphicSerialization,
};

var sut = await RefitGenerator.CreateAsync(settings);
var generatedCode = sut.Generate();
return generatedCode;
}
Comment on lines +270 to +282

Copilot AI Mar 4, 2026

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There is no test coverage for the combination of TrimUnusedSchema = true with oneOf/anyOf + discriminator. The SchemaCleaner runs before ConvertOneOfWithDiscriminatorToAllOf() (in RefitGenerator.CreateAsync vs CSharpClientGeneratorFactory.Create()), which means subtypes are preserved by the cleaner (since it enumerates OneOf/AnyOf entries unconditionally), and the transformation runs afterwards. However, this interaction is not tested. Adding a test with TrimUnusedSchema = true would improve confidence that these two features compose correctly.

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}
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