WEB API response message not shown if no data found?

Question

I try to work with api but the message is not shown when no data found.

This is the controller code:

public HttpResponseMessage GetPatResult(int Patid,int branchid)
{
    using (DBEntities1 entities = new DBEntities1())
    {
        var entity = entities.LAB_RESULTS_CLINIC_VIEW.Where(e => e.Patient_No == Patid && e.branchid==branchid).ToList();
        if (entity == null)
        {
            var message = string.Format("No Results Found ");
            HttpError err = new HttpError(message);
            return Request.CreateResponse(HttpStatusCode.NotFound, err);
           
        }
        else
        {
            return Request.CreateResponse(HttpStatusCode.OK, entity);
           
        }
    }
}

When data are found it shows the data, but when entity == null its not showing the message and shows only this row:

This XML file does not appear to have any style information associated with it. The document tree is shown below. <ArrayOfLAB_RESULTS_CLINIC_VIEW xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.datacontract.org/2004/07/aspnetWEBAPI"/>

How to show message "No Data Found" if data not found?

Also I updated the code from suggested answer link :

asp.net mvc api returning 'This XML file does not appear to have any style information associated with it. The document tree is shown below.'

This is the WebApiConfig file :

public static void Register(HttpConfiguration config)
        {
                 // Web API routes
            config.MapHttpAttributeRoutes();
            config.Formatters.JsonFormatter.SupportedMediaTypes.Add(new System.Net.Http.Headers.MediaTypeHeaderValue("text/html"));
            var appXmlType = config.Formatters.XmlFormatter.SupportedMediaTypes.FirstOrDefault(t => t.MediaType == "application/xml");
            config.Formatters.XmlFormatter.SupportedMediaTypes.Remove(appXmlType);

            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );
      
        }

This is the Global.asax.cs

public class WebApiApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();
            GlobalConfiguration.Configure(WebApiConfig.Register);
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);
            GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
        }
    }

After updated the code its now show [ ] when no data found ?

UPDATE:

I have another controller GetUsers when entityuser == false its showing the message 'User Name or password not Correct' the different between 2 controllers variable entityuser in GetUsers deal as boolean and variable entity in GetPatResult deal as string may be this will affect boolean VS string ?

This is the code of controller GetUsers:

public HttpResponseMessage GetUsers(string username, string password, int branchid)
        {
            using (DBEntities1 entities = new DBEntities1())
            {
                var entityuser = entities.Users_web.Any(user => user.user_name.Equals(username, StringComparison.OrdinalIgnoreCase) && user.user_password == password && user.branch_id == branchid);

                if (entityuser == true)
                {
                    return Request.CreateResponse(HttpStatusCode.OK, entityuser);
                }
                else
                {
                   
                    var message = string.Format("User Name or password not Correct ");
                    HttpError err = new HttpError(message);
                    return Request.CreateResponse(HttpStatusCode.NotFound, err);
                }
            }

        }

UPDATE 2 :

I changed the code in controller GetPatResult to be same code in GetUsers :

var entity = entities.LAB_RESULTS_CLINIC_VIEW.Where(e => e.Patient_No == Patid && e.branchid==branchid).ToList();
                if (entity == null) {} 

to this code

var entity = entities.LAB_RESULTS_CLINIC_VIEW.Any(e => e.Patient_No == Patid && e.branchid==branchid);
                if (entity == true) {}

In this case when no data found message shows , but when data found its not show the data and show only true .

How to fix this issue and show message if no data found and show the data if data found ?

Answer 1

Your "entity" variable is not entity really but a List<Entity>. When no entities are found, it is not null but empty list, and you can check it with (!entity.Any())

    var entity = entities.LAB_RESULTS_CLINIC_VIEW
        .Where(e => e.Patient_No == Patid && e.branchid==branchid)
        .ToList();
    if (!entity.Any())
    {
        var message = string.Format("No Results Found ");
        HttpError err = new HttpError(message);
        return Request.CreateResponse(HttpStatusCode.NotFound, err);
       
    }

If you are going to get single entity or null then call not .ToList() but .FirstOrDefault()

    var entity = entities.LAB_RESULTS_CLINIC_VIEW
        .Where(e => e.Patient_No == Patid && e.branchid==branchid)
        .FirstOrDefault();
    if (entity == null)
    {
        var message = string.Format("No Results Found ");
        HttpError err = new HttpError(message);
        return Request.CreateResponse(HttpStatusCode.NotFound, err);
       
    }

Answer 2

Try to change

var message = string.Format("No Results Found ");
            HttpError err = new HttpError(message);
            return Request.CreateResponse(HttpStatusCode.NotFound, err);

To this

    return Request.CreateResponse(HttpStatusCode.NotFound, "No Results Found");

or better to use modern IHttpActionResult:

public IHttpActionResult GetPatResult(int Patid,int branchid)
{
    using (DBEntities1 entities = new DBEntities1())
    {
        var entity = entities.LAB_RESULTS_CLINIC_VIEW.Where(e => e.Patient_No == Patid && e.branchid==branchid).ToList();
        if (entity == null)
        {
            return NotFound("No Results Found ");
              
        }
        else
        {
            return Ok( entity);
           }
    }
}