o_19mgorv9t13a3ko71fev19l81mqa.pdf

}
}
}
This class defines a new attribute that I have called MustBeTrueAttribute and which overrides the IsValid
method of the base class. This is the method that the model binder will call to validate properties to which the attribute is applied,
passing in the value that the user has provided as the parameter.
The validation logic is simple; a value is valid if it is a bool that has a value of true. I indicate that a value is valid by
returning true from the IsValid method. In Listing 25-14, you can see how I have replaced the Range attribute with the
custom MustBeTrue attribute in the Appointment class.
Listing 25-14. Applying a Custom Validation Attribute in the Appointment.cs File
using System;
using System.ComponentModel.DataAnnotations;
using ModelValidation.Infrastructure;
namespace ModelValidation.Models {
public class Appointment {
[Required]
public string ClientName { get; set; }
[DataType(DataType.Date)]
[Required(ErrorMessage="Please enter a date")]
public DateTime Date { get; set; }
}
}
[MustBeTrue(ErrorMessage="You must accept the terms")]
public bool TermsAccepted { get; set; }
This is neater and easier to make sense of than abusing the Range attribute. You can see the effect of the custom model
validation attribute in Figure 25-8.
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