Check out example codes for "how to validate request body in c#". It will help you in understanding the concepts better.

Code Example 1

[Valid] //here  we apply the filter and request made to this model is validated by validation rules on the model
[HttpPost]
 public HttpResponseMessage someMethod(SomeValidationModel someValidationModel)
 {
    //some logic
 }

// define your Reusable Model validation filter class
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web;
using System.Web.Http.Controllers;
using System.Web.Http.Filters;

namespace mynamespace.filters
{
    public class ValidAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(HttpActionContext actionContext)
        {

            if (!actionContext.ModelState.IsValid)
            {
                actionContext.Response = actionContext.Request.CreateErrorResponse(
                HttpStatusCode.BadRequest, actionContext.ModelState);
            }
        }
    }
}

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