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Cesar Romero · Guest

Im starting to figure out how object validation should work, but no
good design comes to my mind.

I think to implement something like (AOP) aspect, but design only to my
ValueTypes, so I can write the validation in a separeted unit,
register, and when necessary call validation, that will apply the
validation rule in the ValueType.

But I can see a whole picture this, does anyone done something like
that, any paper to suggest?

Thank you in advance.

--
Cesar Romero
http://blogs.liws.com.br/cesar
http://www.liws.com.br/wiki/index.php/English

Joao Morais · Guest

Cesar Romero wrote:

Cesar Romero · Guest

Hechicero · Guest

Hi Cesar,
I may have a sugestion. (I had to design a similar
functionality to let final users customize some validations).

If you want to mimmic some AOP like behaviour for validations
it may come handy the hability to "hook" every method/property of your
domain objects. Then you could write your own validations like "before
executing Person.Age setter validate that the age is between 1 and 99"

In Delphi 7 I achieved a similar behaviour generating a proxy
for each BO, but had some restrictions: each method should be virtual. In
..NET you could take advantage of the proxys that are automatically generated
if you inherit from ContextBoundObject.

Are you planning to do it in Delphi 7 or in a Delphi.NET?

Esteban Calabria

"Cesar Romero" <cesar (AT) liws (DOT) com.br> escribió en el mensaje
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Cesar Romero · Guest

Hechicero · Guest

Cesar,
What we did in delphi 7 to achieve a similar result was to have an
application that automatically generates a proxy for each buisness object.
Unfortunately it has the drawback that each method should be declared
virtual.

Let me give you an example. You have a class:

TPerson = class(TBuisnessObject)
procedure DoSomething;virtual;
procedure DoSomethingElse;virtual;
end;

The proxy generator would automatically generate a

TPersonProxy = class
procedure DoSomething;override
procedure DoSomethingElse;override;
end;

A possible implementation would be:

procedure TPersonProxy.DoSomething;override
Begin
TNotificationServices.getInstance.NotifyBeforeMethodExecution('DoSomething',Self);
inherited;
TNotificationServices.getInstance.NotifyAfterMethodExecution('DoSomething',Self);
end;

and somewhere in your app you could hook

myHook := TMyHook.Create;
TNotificationServices.getInstance.HookMethod('Do*', myHook); //This will
hook every method that starts with Do

Whenever a TPerson is created, a proxy should be created. This can
be achieved overriding TObject.NewInstance class method in your
TBuisnessObject class. (it would be like overriding the classloader in
java).

For this, to code your proxy generator, you may need to get your
hands on a good Object Pascal parser (or code your own). Also you can use
the proxy generator to validate that each object should be virtual.

I think I am not missing anything.

I hope this helps. Tell me if this is info is usefull.

Esteban Calabria

(PD: It would be really really fun to see if you could hook every method
using madCodeHook library and you save from having a proxy for each BO)

"Cesar Romero" <cesarliws (AT) gmail (DOT) com> escribió en el mensaje
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Cesar Romero · Guest

Esteban,

Really usefull, I will start to play with that, and post here my
results, thank you...

--
Cesar Romero
http://blogs.liws.com.br/cesar
http://www.liws.com.br/wiki

Cesar Romero · Guest

Esteban,

All this is really very nice, and I think that works (at least make
sense to me).

This is what I should try, if I need to Proxy any method, But at
moment, my needs is more simple, I forgot to mention that I have a
ValueType Framework done, and my first goal is "inject code" in Get/Set
method of BO properties.

Like this:

TPerson = class(TObjectType, IPerson)
private
FName: IStringType;
protected
function GetName: string;
procedure SetName(const Value: string);
property Name read GetName write SetName;
public
procedure AfterConstruction; override;
end;

procedure TPerson.AfterConstruction;
begin
inherited;
AddMember(FName, 'Name');
end;

function TPerson.GetName: string;
begin
Result:= FName.Value;
end;

procedure TPerson.SetName(const Value: string);
begin
FName.Value:= Value;
end;

For this, I think that I can put the code to hook with "Validator" in

TStringType
GetValue
SetValue

eg:

procedure TStringType.SetValue(const Value: string);
begin
if FValue <> Value then
begin
---> here hook the before set code
FValue:= Value;
Changed;
---> here hoom the after set code
end;
end;

So, for this kind of implementation, I need to create a "Register" for
the object validation methods and the hook code....

But, I still need to have some "IsValid: boolean" function is my BO,
and that I can use your way Smile

And in this particular case, I will put the IsValid function as virtual
in TObjectType, or I still dont know, in a TProxyObjectType, that can
be always created, here your opinion is again welcome. :)

If you want to take a look at my VTF/OPF framework, please take a look
at:
http://www.liws.com.br/wiki/index.php/English
http://jazz.liws.com.br/download/jazz_a4.1.zip (last alpha version)
all your critics and comments are welcome :)

Best regards,

Cesar Romero
http://blogs.liws.com.br/cesar
http://www.liws.com.br/wiki

Hechicero wrote:

Joao Morais · Guest

Cesar Romero wrote:

Cesar Romero · Guest

Joao Morais · Guest

Cesar Romero wrote:

Cesar Romero · Guest