o_19mgorv9t13a3ko71fev19l81mqa.pdf

}
public JsonResult ValidateDate(string Date) {
DateTime parsedDate;
}
}
}
if (!DateTime.TryParse(Date, out parsedDate)) {
return Json("Please enter a valid date (mm/dd/yyyy)",
JsonRequestBehavior.AllowGet);
} else if (DateTime.Now > parsedDate) {
return Json("Please enter a date in the future",
JsonRequestBehavior.AllowGet);
} else {
return Json(true, JsonRequestBehavior.AllowGet);
}
Actions methods that support remote validation must return the JsonResult type, which tells the MVC Framework that I
am working with JSON data, as explained in Chapter 23. In addition to the result, validation action methods must define a
parameter that has the same name as the data field being validated: this is Date for the example. I make sure that I can parse a
DateTime object from the value that the user has submitted and, if I can, check to see that the date is in the future.
Tip I could have taken advantage of model binding so that the parameter to my action method would be a DateTime
object, but doing so would mean that the validation method wouldn’t be called if the user entered a nonsense value like apple,
for example. This is because the model binder wouldn’t have been able to create a DateTime object from apple and throws
an exception when it tries. The remote validation feature doesn’t have a way to express that exception and so it is quietly
discarded. This has the unfortunate effect of not highlighting the data field and so creating the impression that the value that the
user has entered is valid. As a general rule, the best approach to remote validation is to accept a string parameter in the action
method and perform any type conversion, parsing, or model binding explicitly.
I express validation results using the Json method, which creates a JSON-formatted result that the client-side remote
validation script can parse and process. If the value that I am processing meets my requirements, then I pass true as the
parameter to the Json method, like this:
...
return Json(true , JsonRequestBehavior.AllowGet);
...
If I am unhappy with the value, I pass the validation error message that the user should see as the parameter, like this:
...
return Json("Please enter a date in the future" ,
JsonRequestBehavior.AllowGet);
...
In both cases, I must also pass the JsonRequestBehavior.AllowGet value as a parameter. This is because the
MVC Framework disallows GET requests that produce JSON by default, and I have to override this behavior to handle the
validation request. Without this additional parameter, the validation request will quietly fail, and no validation errors will be
displayed to the client.
To use the remote validation method, I apply the Remote attribute to the property I want to validate in the model class. In
Listing 25-25, you can see how I have applied the attribute to the Date property.
Listing 25-25. Using the Remote Attribute in the Appointment.cs File
using System;
688