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CHAPTER 25
Model Validation
In the previous chapter, I showed you how the MVC Framework creates model objects from HTTP requests through the model
binding process. Throughout that chapter, I worked on the basis that the data the user supplied was valid. The reality is that users
will often enter data that isn’t valid and cannot be used, which leads me to the topic of this chapter: model validation.
Model validation is the process of ensuring the data received by the application is suitable for binding to the model and, when
this is not the case, providing useful information to the user that will help explain the problem.
The first part of the process, checking the data received, is one of the key ways to preserve the integrity of the domain model.
Rejecting data that doesn’t make sense in the context of the domain can prevent odd and unwanted states arising in the application.
The second part, helping the user correct the problem, is equally important. Without the information and feedback they need to
interact with the application, users become frustrated and confused. In public-facing applications, this means users will simply
stop using the application. In corporate applications, this means the user’s workflow will be hindered. Neither outcome is
desirable. Fortunately, the MVC Framework provides extensive support for model validation. I will show you how to use the basic
features and then demonstrate some advanced techniques to fine-tune the validation process. Table 25-1 provides the summary for
this chapter.
Table 25-1. Chapter Summary
Problem Solution Listing
Explicitly validate a model Use the ModelState object to record validation errors. 1–7
Generate a summary of validation
errors
Display property-level validation
errors
Use the Html.ValidationSummary helper method. 8–10
Use the Html.ValidationMessageFor helper method. 11
Define validation rules within the model
class
Apply attributes to the properties of the model class. 12
Create a custom validation attribute Derive from the ValidationAttribute class. 13–19
Define a self-validating model Implement the IValidatableObject interface. 20
Use client-side validation Add the Microsoft unobtrusive validation package to the application. 21–23
Perform remote validation
Define an action method that returns a
property to be validated.
JsonResult and add the Remote attribute to the model
24, 25
Preparing the Example Project
For this chapter, I created a new project called ModelValidation using the Visual Studio Empty template, checking the
option to add the core MVC folders and references. Having created the project, I added a new class file called
Appointment.cs, which you can see in Listing 25-1, to the Models folder.
Listing 25-1. The Contents of the Appointment.cs File
using System;
using System.ComponentModel.DataAnnotations;
namespace ModelValidation.Models {
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