How to replace generic type to concrete type when generating Swagger documentation with Swashbuckle?

Question

I have actions decorated with:

[ProducesResponseType(typeof(ValidationException<ErrorEnum>), StatusCodes.Status400BadRequest)]

I need to change the generated response to a different type. So I added an operation filter:

public class ValidationExceptionFilter : IOperationFilter
{
    public void Apply(OpenApiOperation operation, OperationFilterContext context)
    {
        if (context.ApiDescription.ActionDescriptor is ControllerActionDescriptor cad)
        {
            var returnType = cad.MethodInfo.ReturnType;
            if (returnType.IsGenericType && returnType.GetGenericTypeDefinition() == typeof(ValidationException<>))
            {
                var schema = context.SchemaGenerator.GenerateSchema(typeof(ValidationExceptionDto), context.SchemaRepository);
                foreach (var item in operation.Responses["400"].Content)
                    item.Value.Schema = schema;
            }
        }
    }
}

But the generic type is not being replaced when generating the swagger json. What am I missing here?

Answer 1

With This Line you will get the return type of the method:

var returnType = cad.MethodInfo.ReturnType;

For example,A controller like:

[HttpGet]
[ProducesResponseType(400, Type = typeof(Some<WeatherForecast>))]
[ProducesResponseType(200, Type = typeof(WeatherForecast))]
public IEnumerable<WeatherForecast> Get()
{   
.......
}

You would get type of IEnumerable WeatherForecast instead of type of Some or WeatherForecast

I tried to get the ProducesResponseTypeAttribute on the method and access the Type property :

    public class ValidationExceptionFilter : IOperationFilter    
    {        
        public void Apply(OpenApiOperation operation, OperationFilterContext context)        
        {            
        if (context.ApiDescription.ActionDescriptor is ControllerActionDescriptor cad)            
        {                
        var attrs=cad.MethodInfo.GetCustomAttributes(typeof(ProducesResponseTypeAttribute),true);                
        foreach(var attr in attrs)              
        {                   
          if((attr as ProducesResponseTypeAttribute).Type.IsGenericType&& (attr as ProducesResponseTypeAttribute).Type.GetGenericTypeDefinition()==typeof(Some<>))                    {                       
         var schema = context.SchemaGenerator.GenerateSchema(typeof(SomeDto), context.SchemaRepository);                        
        foreach (var item in operation.Responses["400"].Content)                            
        item.Value.Schema = schema;                    
        }                
      }            
     }        
   }    
 }

The Response Type has been modified:

The jsonfile: