C# ASP.NET : show an error message using validations

Question

I want to show validation errors when someone doesn't follow my validation rules (such as too few characters for a first name) or an error when they leave the field empty.

This is an example from my User.cs model class that is showing an error:

[Required(ErrorResponse= "Please do not leave first name field empty")]
[MinLength(4, ErrorResponse = "First name min length is 4")]
public string Firstname { get; set; }

The error I am getting:

Error CS0246: The type or namespace name 'ErrorResponse' could not be found (are you missing a using directive or an assembly reference?)

Answer 1

MinLength doesn't have a ErrorResponse property. I see ErrorMessage property instead.