MVC 3 Custom validation attribute checking against user preference stored in DB

Question

I have a field that may or may not be require based on user preferences which are stored in the database. To handle this I have created a custom validation attribute but I'm not sure how to check to see if the field is actually required based on the user preferences.

I tried setting an "IsRequired" property on my view model via the controller & checking that value in the custom attribute however the property is always false since the validation is firing before the property can be set.

Using data annotations how can I get the "IsRequired" property set before/when the validation kicks off? Should I be checking to see if the field is required once it is already passed to the controller instead of using data annotations?

ViewModel:

Public Class MyViewModel
    <MyCustomValidationAttribute("IsMyFieldRequired")>
    Public Property MyFieldThatMayOrMayNotBeRequired As String
    Public Property IsMyFieldRequired As Boolean

    Public Sub New(objectUsedToSetIsMyFieldRequired As UserPreferences)
        'Set IsMyFieldRequired based on passed in user preferences
    End Sub
End Class

Custom Validation Attribute:

Public Class MyCustomValidationAttribute
    Inherits ValidationAttribute

    Private _otherPropertyName As String

    Public Sub New(otherPropertyName As String)
        Me._otherPropertyName = otherPropertyName 
    End Sub

    Protected Overrides Function IsValid(value As Object, validationContext As System.ComponentModel.DataAnnotations.ValidationContext) As System.ComponentModel.DataAnnotations.ValidationResult
        Dim basePropertyInfo As System.Reflection.PropertyInfo = validationContext.ObjectType.GetProperty(_otherPropertyName)
        Dim isRequired As Boolean = Not CBool(basePropertyInfo.GetValue(validationContext.ObjectInstance, Nothing))
        '
        If isRequired AndAlso value Is Nothing Then Return New ValidationResult(Me.ErrorMessage)
        '
        Return Nothing
    End Function
End Class

Erik Funkenbusch · Accepted Answer · 2011-11-29 17:29:43Z

1

You shouldn't be doing any database access in your validation. You could use remote validation and call an action method to lookup the value, or you could have a property in your model that you set. You can use a variation of the "comparison" custom validation that many people have created. Here's an example http://www.devtrends.co.uk/blog/the-complete-guide-to-validation-in-asp.net-mvc-3-part-2

answered Nov 29, 2011 at 17:29

Erik Funkenbusch

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Billy Over a year ago

The value from the database is actually a property on another class, normally I would pass that class into my view model & it would set the "IsRequired" property or just straight up set the property in my controller. I am not able to do any of this because the validation is occurring prior to my controller action is called. Is there a way to set this property prior to the validation being called? I think I can get the value in the getter of the "IsRequired" property but it doesn't have access to the object w/ that value.

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