Swagger set parameter properties from ASP.Net core

Question

I'm using Swagger with serializing for OpenApi 3.0. In detail I try to serialize an input query parameter array with the following format

?myArray=1,2,3,4

I know how to achieve this in the swagger documentation. Just set parameter.explode=false

parameters:
  - name: myArray
    in: query
    explode: false
    ...

But I don't know how to set this parameter property in ASP.Net Core 3.1 in my controller class to get my swagger doc generated correctly. I tried several things like implementing a filter based on IParameterFilter but nothing worked fine for me.

Answer 1

Fortunately I was able solve the issue as I found a discussion in Swashbuckle.AspNetCore on GitHub.

Implementing a custom parameter filter was the right way.

public class QueryArrayParameterFilter : IParameterFilter
{
    public void Apply(OpenApiParameter parameter, ParameterFilterContext context)
    {
        if (!parameter.In.HasValue || parameter.In.Value != ParameterLocation.Query) 
            return;

        if (parameter.Schema?.Type == "array" && parameter.Name.Equals("myArray"))
        {
            var value = null as IOpenApiExtension;                
            parameter.Extensions.TryGetValue("explode", out value);

            if (value == null)
                parameter.Extensions.Add("explode", new OpenApiBoolean(false));
        }
    }
}

The filter has to be applied to the swagger gen in the ASP.Net core Startup.cs

services.AddSwaggerGen(c =>
{
    c.ParameterFilter<QueryArrayParameterFilter>();
}