Model Validation

Both model binding and model validation occur before the execution of a controller action or a Razor Pages handler method.

Model State

For web apps, it's the app's responsibility to inspect ModelState.IsValid and react appropriately. ModelState represents errors that come from two subsystems: model binding and model validation.

• Errors that originate from model binding are generally data conversion errors. For example, an "x" is entered in an integer field.

• Model validation occurs after model binding and reports errors where data doesn't conform to business rules. For example, a 0 is entered in a field that expects a rating between 1 and 5.

Web API controllers don't have to check ModelState.IsValid if they have the [ApiController] attribute. In that case, an automatic HTTP 400 response containing error details is returned when model state is invalid.

Validation attributes

• [ValidateNever]: Indicates that a property or parameter should be excluded from validation.

• [CreditCard]: Validates that the property has a credit card format. Requires jQuery Validation Additional Methods.

• [Compare]: Validates that two properties in a model match.

• [EmailAddress]: Validates that the property has an email format.

• [Phone]: Validates that the property has a telephone number format.

• [Range]: Validates that the property value falls within a specified range.

• [RegularExpression]: Validates that the property value matches a specified regular expression.

• [Required]: Validates that the field isn't null. See [Required] attribute for details about this attribute's behavior.

• [StringLength]: Validates that a string property value doesn't exceed a specified length limit.

• [Url]: Validates that the property has a URL format.

• [Remote]: Validates input on the client by calling an action method on the server. See [Remote] attribute for details about this attribute's behavior.