Our sample classes already have some attributes that will be checked by the Validation API. For example, in the Destination class, you should already have a MaxLength annotation on the Description property shown here:

[MaxLength(500)]
public string Description { get; set; }

Testing this rule won’t be very easy since breaking it would mean adding a string that is greater than 500 characters. I don’t feel like typing that much. Instead, I’ll add a new MaxLength annotation to another property—the LastName property in the Person class:

[MaxLength(10)]
public string LastName { get; set; }

Now let’s see what happens when we set the length to a string with more than ten characters. GetValidationResult allows you to explicitly validate a single entity. It returns a ValidationResult type that contains three important members. We’ll focus on just one of those for now, the IsValid property, which is a Boolean that indicates if the instance passed its validation rules. Let’s use that to validate a Person instance. The ValidateNewPerson method in Example 6-1 shows calling the GetValidationResult.IsValid method.