Re: API for setting/getting values on Dexterity content

I read your blog and I get your point. I just think direct attribute access
for anything else than the main schema is not possible, be it just because
of ambiguity. That is why I asked how `set_value` and `get_value` should
behave when passed a fieldname :)

Let's see if we can resolve this somehow, instead of bickering whether I've
read you blog or not ;)

-Roel


On 22 October 2014 12:39, Andreas Jung <[email protected]> wrote:

>
> Perhaps you did not read my blog posts or you did not got my point.
>
> The developer experience with Plone and Dexerity - if done the
> right way - is horrible. As developer right now I have to know
> which behavior implements which field in order to set/get
> a value the right way. It is horrible because as a developer
> I want to write pythonic code (translates to attribute access).
> This was also one of the design goals and promises of Dexterity
> as far as I recall. But reality is different. Everyone one write
> Pythonic code but the code is potentially broken (see my rants
> about the plone.app.event implementation).
>
> So the idea - or better the necessity - is to give developers
> a consistent way to read/set values. This means in the first place that
> the whole behavior stuff should be hidden from the developer - at least
> for the standard developer which average skills who is the potential
> user of plone.api. As a developer (e.g. in my current role as writer
> of a fat migration process) I want assign values to an object without
> checking other peoples source code about where a particular attribute
> is defined and check for the related interface. This complexity must be
> hidden in order to writer code in more clear way, in a more reliable way
> and in a more readable way.
>
> The implementation of set/get methods must perform some kind of
> introspection on the schema and the attached behaviors in order
> to retrieve the related interface for adopting the current context
> object. This is of course in some way slower that direct attribute
> access but it is the right way. There is certainly a performance loss
> with this approach but I guess that this could be minimized with
> clever caching of the schema introspection results.
>
> -aj
>
> Roel Bruggink wrote:
> > Hi Andreas,
> >
> > I get what you say. I have a few questions on how this would work in
> > practice, though.
> >
> > Assuming the following:
> > IMySchema():
> > start
> > end
> > name
> > animal_type default='Känguru'
> >
> > IMyFirstBehavior():
> >  start
> >  end
> >  lives_in default='Känguru Island'
> >
> >  IMySecondBehavior():
> >  name default='Jos Henken'
> >
> > How should set_value('start', now()) and get_value('start') behave?
> >
> > Would a dict-like api be of more use, ie obj['IMyBehavior.fieldname'] =
> > 'new value' ? We'll still probably have to adapt the object to that api,
> > though.
> >
> > So in the end, direct attribute access for just the schema itself would
> > work, unless the fieldname is unique between all behaviors.
> >
> > -Roel
> >
> > On 22 October 2014 10:25, Andreas Jung
> > <[email protected]
> > <mailto:[email protected]>> wrote:
> >
> >     Hi there,
> >
> >     the following suggestion is based on former blog posts of mine, e.g.
> >
> >
> https://www.andreas-jung.com/contents/bad-dexterity-application-design
> >
> https://www.andreas-jung.com/contents/copying-dexterity-fields-from-one-instance-to-another-instance
> >
> >     I clearly see a need for an API for safely setting and getting values
> >     for Dexerity content that takes all aspects of behaviors into
> account.
> >     In general: direct attribute access to on Dexterity instance was a
> nice
> >     goal but in reality it is a broken and dangerous programming pattern
> in
> >     Plone right now - unless the direct getting/setting of values through
> >     direct attribute access can be fixed somehow (I think this is very
> >     hard).
> >
> >     The safest way would be to provide methods like
> >
> >     plone.api.content.set_value(obj, fieldname,  value)
> >     value = plone.api.content.get_value(obj, fieldname)
> >
> >     as part of plone.api or through methods of the Dexterity base
> >     classes Item and Container:
> >
> >     obj.set_value(fieldname, value)
> >     value = obj.get_value(fieldname).
> >
> >     The method names are dust and smoke and could be named differently.
> >
> >     Any thoughts on the need for encapsulating the setting/getting of
> value?
> >     Any thoughts where such an API would fit best (plone.api vs. base
> >     classes)?
> >
> >     -aj
> >
> >
> >
> >
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> >
> >
> > --
> > Roel Bruggink
> > http://www.fourdigits.nl/mensen/roel-bruggink
> >
> > Four Digits BV
> > http://www.fourdigits.nl <http://www.fourdigits.nl/> tel: +31(0)26
> 4422700
> >
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-- 
Roel Bruggink
http://www.fourdigits.nl/mensen/roel-bruggink

Four Digits BV
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