Built-in validators

There is a cornucopia of built-in validators in addition to the Equal and NotEmpty validators we’ve seen so far. I won’t provide a comprehensive list (see the documentation) but one of the most interesting is the PredicateValidator validator. This passes the value of the property to a delegate, which can use custom validation logic. This is accomplished with the keyword Must keyword, as shown here:

RuleFor(car => car.Is_Deleted).Must(isDeleted => isDeleted == "0").WithMessage("Car must have value zero");

If this validation fails, the issue is displayed in the results as shown in Figure 5.5:

Figure 5.5 – PredicateValidator error

There is a RegularExpression validator that uses the Matches keyword (instead of Must), but one of my favorites is EmailValidator, which ensures that the value submitted is a valid email. Similarly, there is a CreditCard validator:

RuleFor(cc => cc.CreditCard...