Query parameters miss validation attributes with MicroElements.AspNetCore.OpenApi.FluentValidation

[saithis]

We switched from swagger + MicroElements.Swashbuckle.FluentValidation to microsofts openapi generator + MicroElements.AspNetCore.OpenApi.FluentValidation.

We have a minimal api endpoint with [AsParameters] QueryParameters dto, and this validator:

    public class QueryParametersValidator : AbstractValidator<QueryParameters>
    {
        public RequestDtoValidator()
        {
            RuleFor(x => x.Skip).GreaterThanOrEqualTo(0).WithMessage("'Skip' must be greater than or equal to 0.");

            RuleFor(x => x.Take).InclusiveBetween(1, 100).WithMessage("'Take' must be between 1 and 100.");
        }
    }

Before the generated spec was:

   /api/endpoint: {
      get: {
        parameters: [
          {
            in: query,
            name: Skip,
            required: true,
            schema: {
              exclusiveMinimum: false,
              format: int32,
              minimum: 0,
              nullable: true,
              type: integer
            }
          },
          {
            description: Maximum 100 items can be returned.,
            in: query,
            name: Take,
            required: true,
            schema: {
              description: Maximum 100 items can be returned.,
              exclusiveMaximum: false,
              exclusiveMinimum: false,
              format: int32,
              maximum: 100,
              minimum: 1,
              nullable: true,
              type: integer
            }
          }
        ],

Now it missed the validation properties:

   /api/endpoint: {
      get: {
        parameters: [
          {
            in: query,
            name: Skip,
            schema: {
              format: int32,
              minimum: 0,
              type: integer
            }
          },
          {
            description: Maximum 100 items can be returned.,
            in: query,
            name: Take,
            schema: {
              format: int32,
              maximum: 100,
              minimum: 1,
              type: integer
            }
          }
        ],

For post endpoints with a request body it works just fine, only for query params it doesn't.

[saithis]

I just noticed, that it also doesn't work for nested DTOs:

    public record RequestDto
    {
        // Properties here work fine

        public required CreateAccount Account { get; init; }

        public record CreateAccount
        {
            // Everything in here won't be caught
        }
    }

[avgalex]

Thank you for the detailed report and follow-up about nested DTOs! 🙏

We've published v7.1.4-beta with fixes for both issues:

1. Query parameters with [AsParameters] — added FluentValidationOperationTransformer (IOpenApiOperationTransformer) that applies validation rules to operation parameters. This was missing entirely — only IOpenApiSchemaTransformer was implemented, which only processes component schemas.

2. Nested DTOs in request body — FluentValidationSchemaTransformer was skipping all property-level schemas (context.JsonPropertyInfo != null), but for nested object types like CreateAccount this was the only transformer call. Now it processes property-level schemas for complex types using the property type's own validator.

You can try it out:

dotnet add package MicroElements.AspNetCore.OpenApi.FluentValidation --version 7.1.4-beta

Please let us know if this resolves the issue for your use case!

[saithis]

Wow, that was quick :D
Thanks a bunch, I'll try it out tomorrow (I'm already out of office for today).

[saithis]

It works, thanks! :)

[avgalex]

Fixed in v7.1.4.

Changes:

• Added FluentValidationOperationTransformer — query parameters with [AsParameters] now receive validation constraints
• Fixed nested DTOs in request body not receiving validation constraints