How to find all ModelState errors of a submitted form in ASP.NET Core MVC and Razor Pages

The ModelState class in ASP.NET encapsulates the state of model binding to a property of an action-method argument or to the argument itself, and ModelState.IsValid check is commonly used by the .NET Developers to check whether a web user has submitted a form with all of the necessary details and if they haven't, then the "check" can be used to return some validation errors. 

public async Task<IActionResult> OnPostAsync()

{

    if (!ModelState.IsValid)

    {

        return Page();

    }

    _context.Movies.Add(Movie);

    await _context.SaveChangesAsync();

    return RedirectToPage("./Index");

}

When you have a big form, which you shouldn't have as it is not a great experience for the end users, and if you need to check the model state errors, below is a way to do exactly that. 

ModelState.Values

.SelectMany(x=>x.Errors

.Select(x=>x.ErrorMessage))

.ToList()

This will return all of the ModelState errors and you can then investigate the issue easily and take the necessary action.