Parameter Filter Is Not Called If Operation Was Created From OpenApi Metadata

[warappa]

Parameter filters are only executed if Swagger creates OpenApiOperation from scratch and not by metadata.

The SwaggerGenerator.GenerateOperation calls GenerateOpenApiOperationFromMetadata(...) to get an operation from metadata. If it got one, no filters except the operation filters will be called, because those are in the sub-call-trees of GenerateParameters(...), GenerateRequestBody(...),...

Swashbuckle.AspNetCore/src/Swashbuckle.AspNetCore.SwaggerGen/SwaggerGenerator/SwaggerGenerator.cs

Lines 208 to 216 in 8f363f7

	operation ??= new OpenApiOperation
	{
	Tags = GenerateOperationTags(apiDescription),
	OperationId = _options.OperationIdSelector(apiDescription),
	Parameters = GenerateParameters(apiDescription, schemaRepository),
	RequestBody = GenerateRequestBody(apiDescription, schemaRepository),
	Responses = GenerateResponses(apiDescription, schemaRepository),
	Deprecated = apiDescription.CustomAttributes().OfType<ObsoleteAttribute>().Any()
	};

Please support excuting all filters regardless if there is already openapi metadata available.

[warappa]

Workaround

Here a workaround for those who face the same problem where an operation filter - which gets always called - does the work instead of Swashbuckle:

public class WorkaroundParameterFilterNotCalledOperationFilter : IOperationFilter
{
    private readonly SwaggerGenOptions _options;

    public WorkaroundParameterFilterNotCalledOperationFilter(SwaggerGenOptions options)
    {
        _options = options;
    }

    public void Apply(OpenApiOperation operation, OperationFilterContext context)
    {
        WorkaroundParameterFiltersNotBeingCalled(operation, context);
    }

    private void WorkaroundParameterFiltersNotBeingCalled(OpenApiOperation operation, OperationFilterContext context)
    {
        foreach (var descriptor in _options.ParameterFilterDescriptors)
        {
            var filter = (IParameterFilter)Activator.CreateInstance(descriptor.Type, descriptor.Arguments)!;

            foreach (var parameter in operation.Parameters)
            {
                var desc = context.ApiDescription.ParameterDescriptions.First(x => x.Name == parameter.Name);

                var parameterContext = new ParameterFilterContext(desc, context.SchemaGenerator, context.SchemaRepository, null, desc.ParameterInfo());

                filter.Apply(parameter, parameterContext);
            }
        }
    }
}

Register as usual:

builder.Services.AddSwaggerGen(config =>
{
    config.EnableAnnotations();
    config.OperationFilter<WorkaroundParameterFilterNotCalledOperationFilter>(options);
    // register your parameter filter as usual
    config.ParameterFilter<YourCustomParameterFilter>();
});

[warappa]

Actually the same issue as in Support ParameterFilter and RequestBodyFilter on OpenApiOperation from metadata.

[warappa]

Still an issue with Swashbuckle.AspNetCore 6.5.0 and ASP.NET Core 8.0.1.

[jgarciadelanoceda]

It's fixed with #3059
@martincostello we can close this issue