Today I am continuing exploring WCF RIA Services. I am going to discuss validation in RIA Services.
Any business application needs to validate user input. I am going to start with a simple case. In my sample application a user can enter a company information. I would like to setup RIA Services to force the user to enter a company name before he or she can save the company. In order to do so I am going to use Data Annotations. First of all, I need to add a reference to System.ComponentModel.DataAnnotations DLL to all my projects. RIA Services project should already have the reference.
Now I need to edit my metadata file that corresponds to my data model under .NET version of RIA Services. In my case it is RolodexDomainService.metadata.cs file in SilverlightRIAServicesLibrary.Web project. In that file I need to find Companies class, then location company name property, then decorate the property with required attribute. At the same time we will also put a limit on how many characters a user can enter:
[Required]
[StringLength(30)]
public string CompanyName;
If we want to see the results of our changes, we can run the application, then clear company name for an existing comp-any, then tab out of company name field. Here we get visual feedback that our input was not valid:
Now, let’s create custom validation. Fir example, I am going to force the date added to be no less that 1/1/2000. To do this I will write a custom validation class like so:
public static class ValidationHelper
{
public static ValidationResult DateAddedCheck(DateTime date)
{
ValidationResult result;
if (date > new DateTime(2000, 1, 1))
{
result = new ValidationResult("");
}
else
{
result = new ValidationResult("Date is not valid");
}
return result;
}
}
Validation method that I wrote is a static member. It follows a specific signature that RIA Services requires. For example, it returns Validation Result that contains specific information that validation infrastructure of RIA Services can parse. Overall code is fairly simple.
In order to make this class available on the Silverlight side, I must include my validation class into Silverlight version of RIA Services library – SilverlightRIAServicesLibrary project in my case. In order not to duplicate the code, I will include the same class as a link. I right-click on the project, choose add existing item, navigate to my class, then click on down arrow on Add button, and select Add As Link. Now I have the same validation on both .NET and Silverlight side. To confirm, I just build and run the application. Here is what my DateAdded attributes look like:
[Required]
[CustomValidation(typeof(ValidationHelper), "DateAddedCheck", ErrorMessage = "Date is not valid")]
public DateTime DateAdded;
On important thing to mention that in order to see validation error in UI, we need to update our Binding to look as following:
<TextBox x:Name="CompanyNameTextbox" Grid.Column="1" Grid.Row="0" HorizontalAlignment="Stretch" Margin="6,6,6,6" Text="{Binding Path=CompanyName, Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnExceptions=True}" VerticalAlignment="Center"/>
There is one important thing to notice. If you look at Silverlight side generated code, you will notice that validation occurs before the property value is set. As a result, you cannot rely on property value being set if a validation exception is thrown.
Now, let’s look at saving code that we had to modify in order to validate user input. Here is what it looks like:
try
{
Validator.ValidateObject(this.Model, new ValidationContext(this.Model, null, null), true);
if (this.Model.HasChanges)
{
ShowPleaseWaitMessage();
_context.SubmitChanges(HandleSave, null);
}
}
catch (ValidationException ex)
{
MessageBox.Show(ex.Message);
}
Not really the cleanest code because we have to rely on exceptions being thrown.
I covered all key area of validation, but there is more for you to explore. Please let me know if you have any questions.
