Why Linq-SQL generated code implements INotifyPropertyChanging

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Andrus - 09 Mar 2008 11:15 GMT

I noticed that sqlmetal generated code in northwind.designer.cs implements
two interfaces:

public partial class Customer : INotifyPropertyChanging,
INotifyPropertyChanged {

public string CustomerID {
set {
...
this.SendPropertyChanging();
this._CustomerID = value;
this.SendPropertyChanged("CustomerID");
...

INotifyPropertyChanged alone allows to track changes well at property level.

Why they implemented also INotifyPropertyChanging ? INotifyPropertyChanging
allows to track changes only at entity level and does not even provide
changed property name.
Looks like junk code.

Andrus.

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Frans Bouma [C# MVP] - 09 Mar 2008 11:53 GMT

> I noticed that sqlmetal generated code in northwind.designer.cs
> implements two interfaces:
[quoted text clipped - 17 lines]
> and does not even provide changed property name. Looks like junk
> code.

Try binding a list of entities to a grid or control and you'll quickly
learn that INotifyPropertyChanged is required to make them function
properly together with databinding oriented code.

FB

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Andrus - 09 Mar 2008 12:02 GMT

Frans,

> Try binding a list of entities to a grid or control and you'll quickly
> learn that INotifyPropertyChanged is required to make them function
> properly together with databinding oriented code.

Sure.
However my question was about *INotifyPropertyChanging*
but you replied about *INotifyPropertyChanged*

Andrus.

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Peter Morris - 09 Mar 2008 13:31 GMT

I believe that when you do SQL->LINQ you are able to write code in a partial
class and therefore hook into the part where the property is set, so that
you may implement any required logic.

A quick google should provide some examples.

Pete

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Andrus - 09 Mar 2008 16:58 GMT

>I believe that when you do SQL->LINQ you are able to write code in a
>partial class and therefore hook into the part where the property is set,
>so that you may implement any required logic.

Pete,

Yes, this is possible.
Any idea why MS generated code contains INotifyPropertyChanging
implementation ?
It is not needed for any purpose.

Andrus.

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Jon Skeet [C# MVP] - 09 Mar 2008 17:16 GMT

> >I believe that when you do SQL->LINQ you are able to write code in a
> >partial class and therefore hook into the part where the property is set,
[quoted text clipped - 4 lines]
> implementation ?
> It is not needed for any purpose.

From
https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?
FeedbackID=290470

<quote>
The sole purpose of SendPropertyChanging() was to provide a lightweight
and performant way to detect when an object is changed so that a copy
can be created for keeping original values for use in optimistic
concurrency. Hence, we deliberately did not create event args to ensure
better performance. This is quite different from the traditional
databinding use of INotifyPropertyChanged where the property name is
provided.
</quote>

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Andrus - 09 Mar 2008 21:21 GMT

Jon,

> <quote>
> The sole purpose of SendPropertyChanging() was to provide a lightweight
[quoted text clipped - 5 lines]
> provided.
> </quote>

MS Entity framework seems to generate better code by using

ReportPropertyChanging("SocialSecurityNumber")

sample:

[EdmScalarPropertyAttribute()]
public string SocialSecurityNumber {
get { return _socialSecurityNumber; }

set {
OnSocialSecurityNumberChanging(value);
ReportPropertyChanging("SocialSecurityNumber");
_socialSecurityNumber = value;
ReportPropertyChanged("SocialSecurityNumber");
OnSocialSecurityNumberChanged();
}
}

The ReportPropertyChanging and ReportPropertyChanged methods defer to an
Entity Framework ChangeTracker object that monitors current and original
property values.

So was Microsoft changed their mind in EF ?
Why they are not consistent, implement it differently for Entity framework
!?

Andrus.

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Jon Skeet [C# MVP] - 09 Mar 2008 23:12 GMT

<snip>

> So was Microsoft changed their mind in EF ?
> Why they are not consistent, implement it differently for Entity framework
> !?

Different teams implemented LINQ to SQL and the EF, as far as I'm
aware.

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http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
World class .NET training in the UK: http://iterativetraining.co.uk

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Why Linq-SQL generated code implements INotifyPropertyChanging

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