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Editorial Team
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Asked: 2026-05-20T08:58:08+00:00

So after some experimenting I was surprised to find that this is perfectly acceptable,

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So after some experimenting I was surprised to find that this is perfectly acceptable, in the sense that MVC does not complain about my protected inner abstract Metadata class, and the model validation still works:

Partial Domain Object, generated by a tool:

Partial Public Class SampleDomainObject

    Private _id As Integer
    Private _customCode As String
    Private _description As String

    Public Property ID() As Integer
        Get
            Return Me._id
        End Get
        Set(ByVal value As Integer)
            Me._id = value
        End Set
    End Property

    Public Property CustomCode() As String
        Get
            Return Me._customCode
        End Get
        Set(ByVal value As String)
            Me._customCode = value
        End Set
    End Property

    Public Property Description() As String
        Get
            Return Me._description
        End Get
        Set(ByVal value As String)
            Me._description = value
        End Set
    End Property

End Class

Partial Domain Object, metadata implementation

<MetadataType(GetType(SampleDomainObject.Metadata))> _
Partial Public Class SampleDomainObject

    Protected Friend MustInherit Class Metadata

        <HiddenInput()> _
        Public MustOverride Property ID() As Object

        <Required(), _
        StringLengthRange(4), _
        DisplayName("Custom Code")> _
        Public MustOverride Property CustomCode() As Object

        <Required(), _
        StringLength(255)> _
        Public MustOverride Property Description() As Object

    End Class

End Class

I did this because I didn’t want to have to implement actual properties with backing fields, getters, and setters in VB.NET for the Metadata class to keep the maintenance to a minimum (I’m on .NET 3.5, no auto-properties for me).

What I’m worried about is that having a protected abstract inner class could be confusing to others using this domain object outside of MVC (my domain objects are part of a shared data access framework).

So my question is, in the world of MVC best practices, is this acceptable? Clever even? I’m an MVC newcomer, so I’ll take any feedback I can get.

Thanks!

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1 Answer

  1. Editorial Team

    In Silverlight applications using RIA services, the metadata classes look very similar, minus the MustInherit. I suspect your practices follow suitably good practices, even outside of the context of MVC, considering that the behavior can be seen with MVC and domain services.

    I asked a related question yesterday. The answer describes how this kind of a buddy class strategy works effectively in situations where the domain classes are code-generated. Buddy classes provide protection against code-gen-overwrites. (See Why are buddy classes used for validation?.)

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