Magritte validations may weaken domain model

Hi all,

I'm reading the chapter on magritte in the seaside book and found this
in section 24.5 :

"There are advantages to having your rules outside your domain objects,
[...snip...] Still you have to pay attention since it may weaken your
domain model."

Any pointer to a discussion about the pro/cons of this approach ?
Nothing important, I'm just curious to know...

Cheers,
Francois

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On 2 April 2010 22:10, Francois Stephany <[hidden email]> wrote:
> Hi all,
>
> I'm reading the chapter on magritte in the seaside book and found this in
> section 24.5 :
>
> "There are advantages to having your rules outside your domain objects,
> [...snip...] Still you have to pay attention since it may weaken your domain
> model."

What this means is that it might be better to put the validation
directly into your model.

    MyModel>>isValid
        ^ some complicated condition

Generally there is a trade-off between putting the domain validation
into the model or into the meta-model (as with about anything that can
be part of the meta-model). If you put it into the model it is closer
to the data and behavior and might be easier for people not accustomed
to meta-models; if you put it into the meta-model it is more generic
and can potentially be reused and extended for different models.

Sort of as a workaround you can call the meta-model to do the
validation from the model. Something like:

    MyModel>>isValid
         ^ self description isSatisfiedBy: self

Lukas



--
Lukas Renggli
www.lukas-renggli.ch
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