AW: [Zope3-dev] Re: AW: Re: edit view of a object unknown?

[Jim Fulton]

Roger ineichen wrote:
>>jim wrote:
>>
>>>Jim, if you're lurking :-) could you fill in some of the 
>>
>>pieces here? 
>>
>>>We
>>>had briefly covered some of the factory/initialization issues 
>>>surrounding the add form, but I've already forgotten the details :-o
>>
>>I don't think they are relevent.
>>
>>Roger, I can't really tell what you want to do.  It seems as 
>>though you want to be able to create objects from Python 
>>without knowing anything about their constructors.  This 
>>really only works, in general if the constructors take no arguments.
> 
> 
> Yes. But if somebody write a product this implementation is
> like a chief implementation and other write just a second
> implementation, because they don't whant to use the original.
> And in this way they have to relay on the contructors of them.

Sure, and they need to know how to call these constructors.

...

>>Roger, could you explain what you are trying to do?
> 
> 
> I try:
> First I describe a uscase:
> Let's say we whant use the Object(fields) for to store a class instance
> as a child of a content class. This child is also a content class.
> Both classes have add and edit views. 
> Let's call they question and priority class.
> 
> example:
> class IQuestion
> ----
> class IQuestion(Interface):
>     """aDoc.."""
>     
>     priorities = Tuple(title=_(u'...'),
>         value_type=Object(IPriority, title=u'...'))
> ---
> 
> class Question
> ---
> class Question(Persistent, object):
>     """aDoc.."""
>     priorities = property(get_priorities, set_priorities, None, 'list of
> priorities') 
> ---
> 
> class QuestionEditView
> --- 
> priority_w = CustomWidgetFactory(ObjectWidget, Priority)
> priorities_w = CustomWidgetFactory(SequenceWidget, subwidget=priority_w)
> 
> class QuestionEditView(EditView):
>     __used_for__ = IQuestion
> 
>     priorities_widget = priorities_w
> ---
> 
> 
> In this case we can't add a question in a python method,
> because we don't know which class is used for to add in the 
> property priorities as the value_type. In the example above
> declared with the interface IPriority.

You can add a question if you have an IPriority implementation,
The schema doesn't tell you what that is. There is probably
one stiiting around in the product that provided wuestions,
or you can write one.

> Let's do a little bit more and write a import/export 
> tool which is importing Questions to the Zope3 server
> from a xml file. That's not possible with this information. 

Right, you need some sort of XML schema.

> You have to hard code Priority class in the import/export 
> tool.

Or you can make the tool pluggable, but, at some point,
someone has to decide on a class, just like someone
has to decide on a class when the define an add or edit
form.


 > Here we should call Zope and ask which content object
> implements IPriority. But this could be more then one 
> implementation on this server. ???

Yes

> I think, this system configuration logic which should be
> defined in zcml. 

It depends on the application, I suppose. We haven't needed
this so far.

You could define a factory that produces IPriority objects.
Your import code would then have to scan the registered factories
looking for one that produced the objects you want.

I can imagine some XML/Python conversion framework that could
require specialized registries for mapping xml node types to
Python objects.  You could certainly invent such a registry and
provide new ZCML directives for it.

> For me it's not a problem to implement and import the right
> Priority class if I whould add a Question in a python method. 
> But I whould write more general products and let other
> people decide if the whould implement another Priority class.
> We declare just the interface of IPriority and implement a
> sample Priotity class.

Yes, so they implement a different priority class and used it.
What's the big deal?


> I think if we don't solve this

I still don't know what "this" is. People can always provide
alternate implementations for classes.

 > we whant see many good
> content objects/classes developed by other developer,
> but they will have realy hardcoded relation to other
> content classes if the use Object(fields).

No, object fields specify interface requirements. You can supply
any class you want as long as it satisfies the interface.

 > At least we
> have to write new edit views with the own CustomWidgetFactory.

If you want to use a different class, yes.

> And also they have to implement a own import/export tool for 
> to create the right Priority class in the Question object.

I assume you are refering to XML import/export.  If there was
such an application, it would likely have to provide some mapping
between XML schema definitions and Python objects.  Certainly,
Zope schemas would not be enough, you'd need additional information.
You might very well want a custom registry for that purpose.




> I'm shure if the scripters come to zope we get a lot of nice
> products and the widget framework is really powerfull. 
> They will do creazy things with different content classes in
> a custom widget or in widget wizzards. But you don't have access
> to this information from python methods.

You are right. You won't. <shrug />

> A solution could be;

I still don't see a problem.

> ----------------
> Define a interface 
> Define a class implementation
> Define a edit and add factory
> Define add/edit views (which use the add or edit factory)
> ----------------
> The add and view factories should be accessible from python
> and TTW views. This way you can add or edit the object on each 
> different implemenetation in a general way.

What is an "add and edit" factory? What would it mean?

In your example, would this be a factory for filling in the question
priority field? Or would it be a factory just for creating priorities,
to be used whenevery an IPriority is expected?  What would you do if more
than one factory could be used to create IPriorities? Would you disallow that?
Pick the first one you find?

Jim

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