Values of additionalProperties not transformed

[JTeeuwissen]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

When an endpoint returns a type containing a Dictionary containing another type, the schema of this last type is not processed by schema transformers (see the missing "a": "b" in Bar2 below, causing a new schema to be created).

{
  "schemas": {
    "Bar": {
      "type": "object",
      "properties": {
        "value": {
          "type": "integer",
          "format": "int32",
          "a": "b"
        }
      },
      "a": "b"
    },
    "Bar2": {
      "type": "object",
      "properties": {
        "value": {
          "type": "integer",
          "format": "int32"
        }
      }
    },
    "Foo": {
      "type": "object",
      "properties": {
        "bar": {
          "$ref": "#/components/schemas/Bar"
        },
        "bars": {
          "type": "object",
          "additionalProperties": {
            "$ref": "#/components/schemas/Bar2"
          },
          "a": "b"
        }
      },
      "a": "b"
    }
  }
}

My guess is that additionalProperties should be processed somewhere here:

aspnetcore/src/OpenApi/src/Services/Schemas/OpenApiSchemaService.cs

Lines 172 to 215 in a6ce940

	private async Task InnerApplySchemaTransformersAsync(OpenApiSchema schema,
	JsonTypeInfo jsonTypeInfo,
	JsonPropertyInfo? jsonPropertyInfo,
	OpenApiSchemaTransformerContext context,
	IOpenApiSchemaTransformer transformer,
	CancellationToken cancellationToken = default)
	{
	context.UpdateJsonTypeInfo(jsonTypeInfo, jsonPropertyInfo);
	await transformer.TransformAsync(schema, context, cancellationToken);
	// Only apply transformers on polymorphic schemas where we can resolve the derived
	// types associated with the base type.
	if (schema.AnyOf is { Count: > 0 } && jsonTypeInfo.PolymorphismOptions is not null)
	{
	var anyOfIndex = 0;
	foreach (var derivedType in jsonTypeInfo.PolymorphismOptions.DerivedTypes)
	{
	var derivedJsonTypeInfo = _jsonSerializerOptions.GetTypeInfo(derivedType.DerivedType);
	if (schema.AnyOf.Count <= anyOfIndex)
	{
	break;
	}
	await InnerApplySchemaTransformersAsync(schema.AnyOf[anyOfIndex], derivedJsonTypeInfo, null, context, transformer, cancellationToken);
	anyOfIndex++;
	}
	}
	if (schema.Items is not null)
	{
	var elementTypeInfo = _jsonSerializerOptions.GetTypeInfo(jsonTypeInfo.ElementType!);
	await InnerApplySchemaTransformersAsync(schema.Items, elementTypeInfo, null, context, transformer, cancellationToken);
	}
	if (schema.Properties is { Count: > 0 })
	{
	foreach (var propertyInfo in jsonTypeInfo.Properties)
	{
	if (schema.Properties.TryGetValue(propertyInfo.Name, out var propertySchema))
	{
	await InnerApplySchemaTransformersAsync(propertySchema, _jsonSerializerOptions.GetTypeInfo(propertyInfo.PropertyType), propertyInfo, context, transformer, cancellationToken);
	}
	}
	}
	}

Expected Behavior

I expected to see

{
  "schemas": {
    "Bar": {
      "type": "object",
      "properties": {
        "value": {
          "type": "integer",
          "format": "int32",
          "a": "b"
        }
      },
      "a": "b"
    },
    "Foo": {
      "type": "object",
      "properties": {
        "bar": {
          "$ref": "#/components/schemas/Bar"
        },
        "bars": {
          "type": "object",
          "additionalProperties": {
            "$ref": "#/components/schemas/Bar"
          },
          "a": "b"
        }
      },
      "a": "b"
    }
  }
}

Steps To Reproduce

Add a schema transformer like so:

options.AddSchemaTransformer((schema, _, _)
	=>
{
	schema.Extensions.Add("a", new OpenApiString("b"));
	return Task.CompletedTask;
});

And add an endpoint that returns a type (Foo) which contains a dictionary with another type (Bar).

app.MapGet("/", () => new Foo());

class Foo
{
	public Bar Bar { get; set; }
	public Dictionary<string, Bar> Bars { get; set; }
}

class Bar
{
	public int Value { get; set; }
}

Exceptions (if any)

No response

.NET Version

9.0.200-preview.0.24575.35

Anything else?

No response

[mikekistler]

@JTeeuwissen Thanks for filing this issue!

I followed your instructions for recreate and have reproduced the problem on my side.

I have flagged this as a bug and added it to our backlog.

Also, I think you have identified the right area of the code that needs to be fixed. Would you be interested in submitting a PR with a proposed fix? We welcome community contributions and there are detailed instructions for submitting PRs in the CONTRIBUTING.md file.

[dotnet-policy-service]

Looks like this issue has been identified as a candidate for community contribution. If you're considering sending a PR for this issue, look for the Summary Comment link in the issue description. That comment has been left by an engineer on our team to help you get started with handling this issue. You can learn more about our Help Wanted process here