OpenApi inline enum for query parameters

[dnv-kimbell]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I have an operation with that takes in an enum as query string parameter, and returns it back in the response.

In the parameter section, the enum is just defined as string with no information about what valid values are

"parameters": [
	{
		"name": "e",
		"in": "query",
		"schema": {
			"type": "string"
		}
	}
],

In the response the enum is referenced and it's possible to figure out valid values

"responses": {
	"200": {
		"description": "OK",
		"content": {
			"application/json": {
				"schema": {
					"$ref": "#/components/schemas/EnumWithNoFlags"
				}
			}
		}
	}
}

Expected Behavior

The query parameter should use a reference to the enum schema.

Steps To Reproduce

https://github.com/dnv-kimbell/openapi-inlineschema

Exceptions (if any)

No response

.NET Version

9.0 RC1

Anything else?

No response

[martincostello]

Just spotted this one myself with version 9.0.100-rc.2.24468.2 of the SDK and 9.0.0-rc.2.24470.14 of the M.A.OpenApi library.

With martincostello/openapi-extensions@5742a21 I get an empty enum for CarType:

"CarType": {
  "type": "integer",
  "description": "The type of the car."
}

[captainsafia]

The query parameter should use a reference to the enum schema.

The behavior that I find surprising here is that the schemas generated for the response and the query parameter are different. The schema generated by the query parameter uses a type: string with no enum list configured, whereas the schema configured for the response contains the correct enum listing. The difference in behavior between the two is the actual source of the issue.

Upon further debugging, the issue seemed to only manifest for endpoints that used controller actions (as opposed to minimal APIs) which is particularly strange given that the schema generation logic is shared between the two.

Some further debugging reveals that this might be an issue with the ApiExplorer layer for MVC because the ApiParameterDescription generates a default type of string for this argument:

Based on the logic here. My suspicion gravitated towards the recent changes we made to ModelMetadata to support native AoT since the referenced method interacts with the IsParsable and IsConvertibleType properties that we recently modified as a result of this work although that doesn't appear to be the case.

It seems like the actual root cause is some code that we added in 46b5580 that set the parameter type of simple types (including those that can be parsed from an enum) to string to support the introduction of TryParse binding support in MVC. Ultimately, that appears to be the issue.

Anyhow, I've figured out a bug fix for this that I hope to include in .NET 9 but figured I'd monologue a bit about the root case here for posterities sake.

[captainsafia]

@dnv-kimbell The fix for this has landed in nightly package version 9.0.0-rtm.24476.2.

You'll need to use the following PackageReference:

<PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="9.0.0-rtm.24476.2" />

And make sure that you have a reference to the nightly dotnet9 feed in your nuget.config file:

<add key="dotnet9" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet9/nuget/v3/index.json" />

Can you let me know if that works for you?