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In a wpf application using POCO classes with Entity framework, what is the best way to perform validation on data. I am aware of data annotations but if I am not compeltely wrong they are more used with ASP.Net MVC than WPF (i didnt find many examples with WPF). Earlier I was having my Domain classes implement the IDataErrorInfo interface but I wasnt sure if this was the correct approach. If I would want to share my EntityFramework classes at a later stage with say a silverlight application or an ASP.NET application what would be my best approach so that I can reuse my validation rules. (With ASP.net i believe my IDataErrorInfo way of handling errors would be useless?).I can find a lot of similar questions but not one that particularly meets my needs. It would be great if anyone can point me in the right direction

I have been using T4 templates on my domain model to generate the POCO classes and have been using these POCO class objects as business objects too

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Out of the box, WPF Validation uses IDataErrorInfo and/or ValidationRule's on bindings. IDataErrorInfo being the partial classes that provide a way to tie in additional logic to make sure the value is valid (IE: The Person.Age property is between 1-100) and ValidationRule's being able to inspect the value before it is ever applied to the binding (IE: The Person.Age property is an integer at all). IDataErrorInfo is obviously only helpful when the value of a Binding gets updated with a compatible datatype, ValidationRule's are helpful in the event somebody types "Ten" instead of 10, in your Age textbox and the datatypes are not compatible.

IDataErrorInfo is reusable for all WPF/Silverlight/ASP.NET projects, (see: How to use IDataErrorInfo in ASP.NET)

Whereas ValidationRule's are to be used with Bindings and therefore not useful in a ASP.NET project. They could be considered the equivalent of Javascript validation.

In short, IDataErrorInfo is exactly what you're looking for and will provide the most reuse for those technologies.

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IDataErrorInfo is not supported out-of-the box with EF validation. Annotations are used not only for validation but also can be used to define your model (e.g. Required, MaxLenght, StringLength attributes etc.). Out-of-the box you can use a few more mechanisms to validate your entities - by writing your own attribute by deriving from ValidationAttribute, by using CustomValidationAttribute or by implementing IValidatableObject. That's what EF supports out of the box. If neither of these works for you can replace built-in validation by overwriting DbContext.ValidateEntity() method and use any validation mechanism that works for you. A couple useful links: http://blogs.msdn.com/b/adonet/archive/2010/12/15/ef-feature-ctp5-validation.aspx http://blogs.msdn.com/b/adonet/archive/2011/05/27/ef-4-1-validation.aspx

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