I am currently working on an ASP.NET MVC2 project. This is the first time I am working on a real MVC web application. The ASP.NET MVC website really helped me to get started really fast, but I still have some obscure knowledge concerning datamodel validation.
My problem is that I do not really know where to manage my filled datamodel when it comes to complex validation rules. For example, validating a string field with a Regex is quite easy and I know that I just have to decorate my field with a specific attribute, so data management rules are implemented in the model. But if I have multiple fields that I need to validate which each other, for example multiple datetime that need to be correctly set following a specific time rule, where do I need to validate them? I know that I could create my own validation attributes, but sometimes validation ask a specific validation path which is to complex to be validated using attributes.
This first question also leads me to a related question which is, is it right to validate a model in the controller? Because for the moment that is the only way I found for complex validation. But I find this a bit dirty and I feel it does not really fit a the controller role and much harder to test (multiple code path).
NB: I got some pretty good solutions here but I am waiting for other ideas and some "best practice" solution".
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Mega Subjective. The "where and how to validate with MVC" argument has been beaten to death without coming up with a straight answer.
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This is so subjective and philosophical to each developer/shop that its almost impossible for everybody to agree on anything.
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The other issue is even the validation tooling comes in a bunch of shapes and sizes and can function in different scopes and layers.
Its almost insane the variety in validation tooling.
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How did if( someString != "" ) get so hard? ;). If you read these other answers you'll quickly find there is no best practice at all.
Once you get into Domain Driven Design principals and the discussion on invalid state and objects you'll find the discussion gets even more complicated.. http://stackoverflow.com/questions/134388/where-do-you-do-your-validation-model-controller-or-view. http://stackoverflow.com/questions/2571569/asp-net-mvc-2-validation-using-dtos-instead-of-domain-entities. http://stackoverflow.com/questions/2181940/does-asp-net-mvc-2-validation-need-some-more-thought-in-terms-of-patterns-and-use. http://stackoverflow.com/questions/2075288/. http://stackoverflow.com/questions/1553838/which-validation-library-for-asp-net-mvc. http://stackoverflow.com/questions/294890/asp-net-mvc-user-input-and-service-repository-where-to-do-validation. http://stackoverflow.com/questions/1558457/asp-net-mvc-is-data-annotation-validation-enough. http://stackoverflow.com/questions/25675/mvc-where-to-implement-form-validation-server-side. http://stackoverflow.com/questions/1531388/asp-net-mvc-validation. DDD:. http://stackoverflow.com/questions/516615/validation-in-a-domain-driven-design.
. Sure, you can do some simple validation in the view such as Required, Regex rules and so on.. Complex business rules should sit inside a business entity or some business logic layer.. What I do in my MVC projects is have the model call a method such as Validate() which will check the final level of validation such as business rules and so on and then I can call Save();.