For separation of concern, I would suggest you use action filter for model validation, so you don’t need to care much how to do validation in your api controller:
using System.Net;
using System.Net.Http;
using System.Web.Http.Controllers;
using System.Web.Http.Filters;
namespace System.Web.Http.Filters
{
public class ValidationActionFilter : ActionFilterAttribute
{
public override void OnActionExecuting(HttpActionContext actionContext)
{
var modelState = actionContext.ModelState;
if (!modelState.IsValid)
actionContext.Response = actionContext.Request
.CreateErrorResponse(HttpStatusCode.BadRequest, modelState);
}
}
}