Magritte pre-validation hooks?

Is there an easy way in Magritte to clean up user-supplied data  
before validation? I'm doing something like this:

> Address>>state: aString
> state := aString ifNotNil: [:s | s trimBlanks]
>
> Address class>>descriptionState
> ^(MAStringDescription auto: 'state' label: 'State')
> addCondition: [:value | value trimBlanks size = 2] labelled:  
> 'Please enter a two-character abbreviation';
> yourself

In Rails, ActiveRecord offers a before_validation hook for this kind  
of cleanup. I have mostly used it to coerce empty strings to nil, but  
it looks like Magritte's default string reader at least does that  
part for me.

Should I implement my own StringReader to accomplish this in one place?

--
Ken Treis
Miriam Technologies, Inc.


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There is no such thing in Magritte. Of course there are many places  
where you could introduce such a thing. The StringReader is something  
else, it transforms a string to a real object (e.g. a date object, a  
number, etc).

It would be probably the best if you create a new mechanism, similar  
to the one of the StringReader, that is responsible to do that?

Lukas

--
Lukas Renggli
http://www.lukas-renggli.ch



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On Jun 2, 2007, at 1:02 AM, Lukas Renggli wrote:

Hi Lukas,

Even though Rails implements something more generic (pre-validation  
hooks where any transformation could happen), I realized that I  
really only needed it for this one specific situation (trimming  
blanks off of strings and coercing them to nil if they are empty).

So I implemented my own StringReader subclass that overrides one method:

PruningStringReader>>visitStringDescription: aDescription
        | trimmed |
        trimmed := self contents trimBlanks.
        self object: (trimmed isEmpty ifTrue: [nil] ifFalse: [trimmed])

This solves the problem that set me out on this quest in the first  
place. I'm using this as my default string reader, since I can't  
think of any situations in my apps where leading or trailing blanks  
would be significant.

Thanks,

--
Ken Treis
Miriam Technologies, Inc.


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