Custom State

There may be an occasion where you'd like to return contextual information about the state of your validation rule when it was run. The WithState method allows you to associate any custom data with the validation results.

We could assign a custom state by modifying a line to read:

public class PersonValidator : AbstractValidator<Person> 
{
  public PersonValidator() 
  {
    RuleFor(person => person.Surname).NotNull();
    RuleFor(person => person.Forename).NotNull().WithState(person => 1234);  
  }
}

This state is then available within the CustomState property of the ValidationFailure.

var validator = new PersonValidator();
var result = validator.Validate(new Person());
foreach (var failure in result.Errors) 
{
  Console.WriteLine($"Property: {failure.PropertyName} State: {failure.CustomState}");
}

The output would be:

Property: Surname State:
Property: Forename State: 1234

By default the CustomState property will be null if WithState hasn't been called.

FluentValidation/docs/custom-state.md

Custom State