Change Value in LINQ-to-SQL OnPropertyChanging Partial Method

Question

Hi everyone.
Im trying to modify a value in my BLL via using linq2sql's partial method which is fired when that specific property is edited by user
specifically i want to set the "cell" field to a full canonical-formatted cell(mobile) number

here is my code which gets fired

Private Sub OnCellChanging(ByVal value As String)
        value = Regex.Replace(value, "\+| |\(|\)|-", "")
        value = MiniCanon(value)
    End Sub

the problem is that the new "value" value is not persisted back to the db. the code fires alright and the local "value" variable gets the new string which i want. but it just gets lost as soon as the code exists.
i tried putting

Cell=minicanon(value)

but that puts code in an endless loop
what can be done?
thanks

Answer 1

Hi YismanOl,

You can try to replace 'ByVal' with 'ByRef' to see if it works. In fact, you can refer to the partial methods generated by the OR designer. Compare yours with the machine-generated code and find out the difference. I hope this might help  you.

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Best regards,
Charlie Lee

Please remember to mark the replies as answers if they help and unmark them if they provide no help.

Answer 2

Hi Zhipeng Lee
i appreciate your posting
i tried both suggestions
1: putting ByRef in my partial method resulted in the following compilation error:
Private Sub OnCellChanging(value As String)' and 'Private Sub OnCellChanging(ByRef value As String)' cannot overload each other because they differ only by parameters declared 'ByRef' or 'ByVal'.
2: so i had a look at the partial method in the orm designer. it looks like this:

Partial Private Sub OnCellChanging(value As String)
End Sub
Partial Private Sub OnCellChanged()
End Sub

it does not show byref or byval thought that usually means byval.
if so, it the exact same signature like my own method
the basic problem is that these methods are empty, so i cant know how it would assign values to properties

please reply with some more advice
i appreciate your help very much
all the best

Answer 3

Hello,

Scott Gu has a great blog series on Linq to Sql and has provided various examples on anything linq related.

The link here: http://weblogs.asp.net/scottgu/archive/2007/07/11/linq-to-sql-part-4-updating-our-database.aspx

Under the

Custom Property Validation Support

He provides good examples of custom property changing validation just like what you are doing but his example are in csharp (should not be a problem converting to vb.net)

I don't know if any of this is relevant to your problem but it could help in troubleshooting your problem!

Hope this helps!

Answer 4

Thank you d13mr3m1x

But no, scotts examples as well as most examples on the web, only use the OnChanging method for validation. He does not change the value or set it in any way. I'm afraid the question is stil open

I still appreciate your joining and taking the time to answer.

Any other ideas? Anyone?

Thank you all

Answer 5

Hi Yisman,


The OnPropertyChanging partial methods aren't meant for changing the value, thats why the new value is passed by value and not by reference. This event occurs when you have decided that the value WILL change. The only thing you can do in your OnPropertyChanging() methods is that you can throw a ValidationException() (or any other appropriate exception) if you don't want the value to be changed.

In this scenario where you want to format the given cell number, an option would be to create another property wrapper (in a partial class) in which you format and set the underlying Cell property like this:

Public Property RawCellNumber() As String
Get
  ' you may return the formatted Cell No. here
End Get
Set
  ' set the underlying Cell property after applying regex
  Me.Cell = Regex.Replace(value, "\+| |\(|\)|-", "")
End Set
End Property

Hope that helps.

Regards,

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Syed Mehroz Alam
My Blog | My Articles

Answer 6

As Syed says, better have a separate property that does the regex modifications etc. But if you really must do it in OnCellChanging, just add a class level private flag to avoid a forever recursive thing. E.g.:

private bool _inCellChanging = false;

Private Sub OnCellChanging(ByVal value As String)
  if (_inCellChanging == false) then
    _inCellChanging = true;
    value = Regex.Replace(value, "\+| |\(|\)|-", "")
    Cell = MiniCanon(value)
    _inCellChanging = false;
  end if
End Sub

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Kristofer - Huagati Systems Co., Ltd.
Cool tools for Linq-to-SQL and Entity Framework:
huagati.com/dbmltools (add-in with new features for Visual Studio 2008's L2S and EF designers)
huagati.com/L2SProfiler (Query profiler for Linq-to-SQL and LLBLGen Pro)

Answer 7

thank you all for the great ideas

either 1 requires extra coding. (this is something i might want to do on many properties) so if Syed is correct, which definetly seems so. then i would probably have to go with the OnValidate method. which might be inefficient. cause i will be modifying the cell field at any update of the row. but it seems the most maintainable solution as of now.

even though KristoferA's solution is pretty clean as well. it does require an extra boolean and several lines PER property. but it just might work out

I thank you all for chipping in. i marked your posts as helpful, but still open to additional ideas

all the best

Answer 8

hi
i just now got around to trying your code, but unfortunatley it does not work. here is the code im using:

Dim IsCellChanging As Boolean
    Private Sub OnCellChanging(ByVal value As String)
        If Not IsCellChanging Then
            IsCellChanging = True
            Cell = MiniCanon(Regex.Replace(value, "\+| |\(|\)|-", ""))
            IsCellChanging = False
        End If
    End Sub

the new value holds a bit longer then w/o your local variable. but still it gets lost somewehre thru the iterations. in the end when it is submitted to db, it is revreted to its original value, before my "canonization".

did i translate the c# correctly? i think i did
all the best

Answer 9

Try using the partial method for OnCellChanged instead of OnCellChanging. OnCellChanging happens before the property value is set, so after this method returns the property setter will overwrite the canonicalized value that you create here. The only difference between the methods is that you will not get any parameters, so instead you can do this:

Cell = MiniCanon(Regex.Replace(Cell, "\+| |\(\)|-", ""))

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Blog - http://blogs.rev-net.com/ddewinter/ Twitter - @ddewinter