PropertyValidators: Conditions

When

If you want that one check is executed only with certain condition, you can use When method:

builder.RuleFor(vm => vm.Email)
    .NotEmpty()
        .When(vm => PhoneNumber, phoneNumber => string.IsNullOrEmpty(phoneNumber))
    .Must(IsValidEmail);

In this case, it's possible to have empty Email when property PhoneNumber is not empty (we check NotEmpty only if PhoneNumber is empty). This rule will be revalidated each time when PhoneNumber changed. So if you enter phone number and then deleted it -> property Email will be not valid.

AllWhen

If you want that all checks are executed only with certain condition, you can use AllWhen method:

builder.RuleFor(vm => vm.Country)
    .NotEmpty()
    .MaxLength(64)
    .AllWhen(vm => vm.ShouldSpecifyAdditionalInformation);

In this case property Country can have any value if property ShouldSpecifyAdditionalInformation == false.

Create custom condtion

There are few overloading of methods When and AllWhen, but you can create your own with interface ReactiveValidation.Validators.Conditions.IValidationCondition.

If your condition connected with some other properties, their expressions should be at IValidationCondition.RelatedProperties.

You can use FuncValidationCondition as sample.