How can I handle validation errors in ASP.NET MVC?

How can I handle validation errors in ASP.NET MVC?

In ASP.NET MVC, you can handle validation errors using data annotations and model state validation. When a model fails validation, you can check the ModelState.IsValid property in your controller action.

Can you give me an example of using data annotations?

Sure! You can use attributes like [Required], [StringLength], and [Range] on your model properties to enforce validation rules. For example:

public class UserModel {
    [Required(ErrorMessage = "Name is required.")]
    public string Name { get; set; }

    [Range(18, 100, ErrorMessage = "Age must be between 18 and 100.")]
    public int Age { get; set; }
}

What happens if the validation fails?

If validation fails, the ModelState will contain errors, and you can return the same view with the validation messages. You can access the errors using ModelState.Values.

How can I display these validation messages in the view?

You can display validation messages in your view using the Html.ValidationMessageFor helper. For example:

@Html.ValidationMessageFor(model => model.Name)