Original value tracking

JoeFallon1 posted on Thursday, July 03, 2008

I am trying to implement the original value tracking that was discussed in this thread:
http://forums.lhotka.net/forums/5/19925/ShowThread.aspx

But I am having a bit of trouble.

1. When DataPortal_Fetch is called the defaultValue is first set and THEN the value from the database is set. So it takes 2 passes to get the correct original value.

2. But when DataPortal_Create is called, the default Value could be the Original value unless the BO developer sets it to something else. So in this case it is either 1 or 2 passes depending on how the BO is configured. The code below is not reliable enough to handle both cases.

Patrick's idea was to have the PropertyInfo object passed in to the constructor of the FieldData class *along with the Original Value*. But where did the PropertyInfo class get the Original value??

So I guess my question is: Is there a better way to track the Original value?

<Serializable()> _
Public Class MyFieldData(Of T)
  Inherits FieldData(Of T)
  Implements IFieldData(Of T)

  Private _origdata As T
  Private _hasBeenSet As Integer = 0
  Private _trackOrigValue As Boolean = False

  Public Sub New(ByVal name As String, Optional ByVal trackOrigValue As Boolean = False)
    MyBase.New(name)
    _trackOrigValue = trackOrigValue
  End Sub

  Public Overrides Property Value() As T
    Get
      Return MyBase.Value
    End Get

    Set(ByVal value As T)
      MyBase.Value = value 'sets IsDirty = True

      'When a BO is Fetched from the DB, the framework sets the DefaultValue first and THEN sets the DB value.
      'So the first time it is set is not the correct time to flip the flag!
      'What about when DP_Create is called? Then setting the default value is the correct place to set the flag!
      If _trackOrigValue AndAlso _hasBeenSet <= 1 Then 'only set the original value once.
        _origdata = value
        _hasBeenSet += 1
      End If

      If _trackOrigValue AndAlso MyBase.Value.Equals(_origdata) Then
        MarkClean() 'sets IsDirty to False
      End If
    End Set
  End Property

  Public ReadOnly Property OrigValue() As T
    Get
      Return _origdata
    End Get
  End Property

  Public Overrides ReadOnly Property IsDirty() As Boolean
    Get
      If _trackOrigValue AndAlso MyBase.Value.Equals(_origdata) Then
        Return False
      Else
        Return MyBase.IsDirty
      End If
    End Get
  End Property

End Class

Joe