如何修改只读LINQ属性

我有一个Linq to SQL生成的类,它具有只读属性:

<Column(Name:="totalLogins", Storage:="_TotalLogins", DbType:="Int", UpdateCheck:=UpdateCheck.Never)>  _
Public ReadOnly Property TotalLogins() As System.Nullable(Of Integer)
    Get
        Return Me._TotalLogins
    End Get
End Property

这可以防止它在外部进行更改,但我希望从类中更新该属性,如下所示:

Partial Public Class User

...

    Public Shared Sub Login(Username, Password)
        ValidateCredentials(UserName, Password)

        Dim dc As New MyDataContext()
        Dim user As User = (from u in dc.Users select u where u.UserName = Username)).FirstOrDefault()
        user._TotalLogins += 1
        dc.SubmitChanges()
    End Sub

...

End Class

但是对用户的调用。_totallogins+=1没有被写入数据库?对如何让Linq看到我的变化有什么想法吗?