What is the point of the key parameter in ModelState.AddModelError in ASP.NET MVC?

Question

I\'ve added validation checks in my controller that modify the ModelState if the validation fails.

For example:

Answer 1

Actually you can set any validation message while your form submission unsuccessful suppose you make a field in model

[Required]
    [DataType(DataType.Password)]
    [Display(Name = "Current password")]
    public string OldPassword { get; set; }

and while your modelState got invalid you can set error message bind with that field like as.

ModelState.AddModelError("OldPassword", "Current Password do not match ");

then your error message will be bind with field in model named "OldPassword"