How to return JsonResult through generic Func<T>?

Question

Having an Action that uses a base method that expect a Func

public class HomeController: BaseController
{
    public JsonResult HomeController()
    {
        var model =  ExecuteHandledJTableJsonOperation(() =>
            {
               //do some stuff
            }, LocalResources.CommonErrorMessage);
        return Json(model);
    }
}

And the base method that expect Func

public class BaseController : Controller
{
    public T ExecuteHandledJTableJsonOperation<T>(Func<T> actionToExecute, string errorMessage)
    {
        try
        {
            return actionToExecute.Invoke();
        }
        catch (Exception ex)
        {
            LogEntry entry = new LogEntry();
            entry.AddErrorMessage(ex.Message);
            entry.AddErrorMessage(String.Format("Inner Exception:", ex.InnerException.Message));
            //entry.Message = ex.Message;
            entry.Priority = 1;
            entry.EventId = 432;
            entry.Severity = System.Diagnostics.TraceEventType.Error;
            writer.Write(entry);
            return Json(new { Result = "ERROR", Message = errorMessage });
        }
    }
}

It retrieves me an error when I trying to return Json(new { Result = "ERROR", Message = errorMessage });

Cannot implicitly convert type 'System.Web.Mvc.JsonResult' to 'T'

I know that is better if I create an override of ExecuteHandledJTableJsonOperation that expect two action, one to execute/return normally and the second to execute when the operation has an excetion.

Something like this:

return ExecuteHandledJTableJsonOperation(() =>
{
    //do something
    return Json(new { Result = "OK", Records = excepciones, TotalRecordCount = excepciones.Count() });
}, () =>
{
    return Json(new { Result = "ERROR", Message = Properties.Resources.CommonErrorMessage });
});

But I want to know how to solve the first case: Cannot implicitly convert type 'System.Web.Mvc.JsonResult' to 'T'
Thanks.

Answer 1

It is not entirely clear why your method is generic as you seem to want to always return a JsonResult as such simply change your method to this.

public class BaseController : Controller
{
    public JsonResult ExecuteHandledJTableJsonOperation<T>(Func<JsonResult> actionToExecute, string errorMessage)
    {
        try
        {
            return actionToExecute.Invoke();
        }
        catch (Exception ex)
        {
            LogEntry entry = new LogEntry();
            entry.AddErrorMessage(ex.Message);
            entry.AddErrorMessage(String.Format("Inner Exception:", ex.InnerException.Message));
            //entry.Message = ex.Message;
            entry.Priority = 1;
            entry.EventId = 432;
            entry.Severity = System.Diagnostics.TraceEventType.Error;
            writer.Write(entry);
            return Json(new { Result = "ERROR", Message = errorMessage });
        }
    }
}

Answer 2

I guess you don't need that to be soo generic. Providing that you will use that only in your actions you can return ActionResult as JsonResult derived from it. Think adding constraint of ActionResult will be sufficient in your case:

public T ExecuteHandledJTableJsonOperation<T>(Func<T> actionToExecute, string errorMessage) 
    where T: ActionResult
{
    //code
}