CODEWITHSUNDEEP
asp.net-mvcmodel-view-controllervalidationdata-annotationsmodel-binding
Marko
Marko

Reputation: 13233

MVC Model binding / validation

After a year or so of MVC experience I'm still confused about one thing: How to effectively use the DataAnnotations with ModelState.IsValid? For simple tutorial example this all works just fine and I have no questions about that. But supposed I have the following model:

Public Class Movie

    Public Property MovieID As Integer
    Public Property Title As String
    Public Property Year As Integer
    Public Property AddedByUser As String

End Class

Now the field AddedByUser is required in the database however I don't want the user to provide this but rather the business logic based on the currently logged in user. How would I use the DataAnnotation attributes for this scenario? If I make this field required then in the controller when I say:

 Public Function SaveMovie(ByVal entity as Movie) As ActionResult
    If ModelState.IsValid
       // Save to DB here...
    End If
    Return View(entity)
 End Function

... the validation will fail because I don't have that field in the view bindings. Should I have a hidden field for this? Should I write a custom view model for SaveMovie action? I suppose I could write my own validation in business logic but then why use model validation at all? Custom model binder perhaps? What is the best way to handle these types of scenarios?

Just to give another example scenario what about the difference between insert and update operation and validation? For update operations object's primary key is required. However that is not the case for inserts. Are you supposed to have separate models for insert and update just because of this one key property?

Upvotes: 1

Views: 746

Answers (1)

Webcognoscere
Webcognoscere

Reputation: 1822

so the way that I handle this is I use the DataAnnotation based validation for user input type stuff. i.e. Validation on email addresses, dates, required fields etc. Stuff that you need a quick 'sanity check' on and need to double check the users entries on.

I don't put any DataAnnotations on the fields that my Database controls or my code controls, i.e. Primary Keys, your [AddedByUser] property as the user doesn't access these properties directly and so you shouldn't have to add validation checks on this. Since your code is the only thing that updates these properties, why validate them?

For more 'business rule' type validation I implement IValidatableObject on my model which gets run, in MVC, after all property-level validations have succeeded. Note that it won't run if the property-level validations fail. And this makes sense, because if the data is 'dirty' you wouldn't want to proceed to run more complex validation etc.

Hope this helps :)

Upvotes: 1

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