Swagger - Web API - Optional query parameters

This worked for me:

[System.Web.Http.HttpGet] 
[Route("api/DoStuff/{reqParam}")]  
[Route("api/DoStuff/{reqParam}/{optParam1:alpha?}/{optParam2:datetime?}")]
public string Get(string reqParam, string optParam1= "", string optParam2= "")

It did create two sections in my Swagger UI but that works for me.

The way Swagger works it pulls out parameters based on your signature of Action i.e parameters to your Action, but here you are getting these value from ControllerContext which obviously Swagger will never be aware of.

So You need to change the signature of the Action and pass your parameters there.

They will be treated as optional if you make them of nullable type -

[HttpGet]
[Route("students")]
[SwaggerOperation(Tags = new[] { "Student" })]
[SwaggerResponse(HttpStatusCode.OK, Type = typeof(ResponseModel<IList<Student>>))]
[SwaggerResponseExample(HttpStatusCode.OK, typeof(StudentResponseExample))]
[SwaggerResponse(HttpStatusCode.InternalServerError)]
public IHttpActionResult SearchStudent(long? SyncDate = null,int? OffSet = null,int? Limit = null)
{
    // Use the variables here
    .
    .
    .

}