How can I use data annotations in ASP.NET MVC?

How can I use data annotations in ASP.NET MVC?

You can use data annotations to enforce validation rules on your model properties in ASP.NET MVC. For example, you can use attributes like [Required], [StringLength], and [Range] to specify validation criteria.

Can you give me an example of using the [Required] attribute?

Sure! If you have a model class like this:

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

The [Required] attribute ensures that the Username property must be filled out.

What happens if the validation fails?

If validation fails, the model state will be invalid, and you can check this in your controller. You can return the user to the form with error messages displayed.

Are there other data annotations I should know about?

Yes, there are several useful data annotations like [EmailAddress], [Phone], and [RegularExpression] that help with different types of validation.