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Silverlight 4 + RIA Services - Ready for Business: Validating Data

A look at data validation in our business applications

To continue our series let’s look at data validation our business applications. Updating data is great, but when you enable data update you often need to check the data to ensure it is valid.  RIA Services as clean, prescriptive pattern for handling this.   First let’s look at what you get for free.  The value for any field entered has to be valid for the range of that data type.  For example, you never need to write code to ensure someone didn’t type is “forty-two” into a textbox bound to an int field. You also get nice looking and well behaved validation exposure in the UI.

image_thumb[82]

Note: if you are not seeing this, ensure that “ValidatesOnExceptions=True” is in the binding expression for the each field

Of course, that sort of validation only goes so far, in  real application you need some more extensive validation.  And for this validation you absolutely have to check the validation before your business logic is run because you don’t know what client might be sending you the update, in addition, you want to check the validation on the client to give the user a really nice user experience and reduce the number of error-case hits to your server which reduces server load.   In traditional models, you need do error checking twice to cover both of these cases.  But that is obviously error prone and easy to get out of sync.  So RIA Services offers a common model for validation.

The most common cases are covered by a set of custom attributes you apply to your model on the server.  These attributes are common across the .NET Framework supported by ASP.NET Dynamic Data, ASP.NET MVC and RIA Services.  You can find the full set in System.ComponentModel.DataAnnotations.    But to give you a flavor:

[Display(Order = 0)]
[Required(ErrorMessage = "Please provide a name")]
public string Name { get; set; }

[Range(0, 999)]
public Nullable<decimal> Price { get; set; }

[RegularExpression(@"^http\://[a-zA-Z0-9\-\.]+\.[a-zA-Z]{2,3}(/\S*)?$",
                    ErrorMessage = "Please use standard Url format")]
public string Uri { get; set; }

 

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As you an see from above the validations on the client are handled automatically, but they are also run again on the server BEFORE your Update method is called.  This allows you to keep the validation gunk out of your business logic for Update.   The other great thing is that these validations will apply in exactly the same way no mater where that entity is used in the UI because they are build into the model.    You can of course localize the error messages by passing a resource ID rather than a hard code string.  You can also read these validation metadata out of an external config file or database rather than using attributes in the code.

But clearly that doesn’t cover all cases.  Many times you need to write some actual procedural code.  Let’s consider an example of validating the description to ensure it is really complete.  There is no custom attribute for that ;-).  So let’s write a bit of C# code.  First we need to indicate that the Description field has some custom validation.

Read the original blog entry...

More Stories By Brad Abrams

Brad Abrams is currently the Group Program Manager for the UI Framework and Services team at Microsoft which is responsible for delivering the developer platform that spans both client and web based applications, as well as the common services that are available to all applications. Specific technologies owned by this team include ASP.NET, Atlas and Windows Forms. He was a founding member of both the Common Language Runtime, and .NET Framework teams.

Brad has been designing parts of the .NET Framework since 1998 when he started his framework design career building the BCL (Base Class Library) that ships as a core part of the .NET Framework. He was also the lead editor on the Common Language Specification (CLS), the .NET Framework Design Guidelines, the libraries in the ECMA\ISO CLI Standard, and has been deeply involved with the WinFX and Windows Vista efforts from their beginning.

He co-authored Programming in the .NET Environment, and was editor on .NET Framework Standard Library Annotated Reference Vol 1 and Vol 2 and the Framework Design Guidelines.

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