AspNetCore.Docs/aspnetcore/includes/RP-MVC/validation-net6.md

Add validation rules to the movie model

The DataAnnotations namespace provides a set of built-in validation attributes that are applied declaratively to a class or property. DataAnnotations also contains formatting attributes like DataType that help with formatting and don't provide any validation.

Update the Movie class to take advantage of the built-in Required, StringLength, RegularExpression, and Range validation attributes.

[!code-csharp]

The validation attributes specify behavior that you want to enforce on the model properties they're applied to:

• The Required and MinimumLength attributes indicate that a property must have a value; but nothing prevents a user from entering white space to satisfy this validation.

• The RegularExpression attribute is used to limit what characters can be input. In the preceding code, "Genre":

  • Must only use letters.
  • The first letter is required to be uppercase. White spaces are allowed while numbers, and special characters are not allowed.

• The RegularExpression "Rating":

  • Requires that the first character be an uppercase letter.
  • Allows special characters and numbers in subsequent spaces. "PG-13" is valid for a rating, but fails for a "Genre".

• The Range attribute constrains a value to within a specified range.

• The StringLength attribute lets you set the maximum length of a string property, and optionally its minimum length.

• Value types (such as decimal, int, float, DateTime) are inherently required and don't need the [Required] attribute.

Having validation rules automatically enforced by ASP.NET Core helps make your app more robust. It also ensures that you can't forget to validate something and inadvertently let bad data into the database.