[Zope-CMF] Extending FTI.isConstructionAllowed

[Tres Seaver]

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Wichert Akkerman wrote:
> Previously Tres Seaver wrote:
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>> Wichert Akkerman wrote:
>>> I have a use case where I need to put additional restrictions on object 
>>> creation, in particular I need to restrict the maximum depth of items 
>>> inside of a container of a specific type. The ideal place to put such a 
>>> restriction seems to be the isConstructionAllowed method on the FTI. 
>>> Currently this method is not very extensible, which leads to complicated 
>>> code in various FTI types.
>>>
>>> I am considering to add an extension point here, something like this:
>>>
>>> class ITypeConstructionFilter(Interface):
>>>      def __init__(fti, container):
>>>          """Adapt on the FTI of the object being created and the target 
>>> container"""
>>>
>>>      def allowed():
>>>          """Check if construction is allowed."""
>>>
>>>
>>> current checks such as the workflow check that was added in CMF 2.2, or 
>>> the type constraint logic Plone has in ATContentTypes could be moved to 
>>> such an adapter. The standard isConstructionAllowed method could then 
>>> query all registered adapters to check if construction should be possible.
>>>
>>> Does this sound sensible?
>> I'm not sure about querying all adapters:  I think it would be clearer
>> to query the one adapter whose name corresponds to the type name of the
>> FTI (the "query all" case leads to tricky / emergent behavior).
> 
> Querying a single adapter makes it very hard to use this as an extension
> point. Being able to have multiple independent validation-hooks is the
> whole point of my suggestion, and being able to only use a single
> adapter would make that impossible.

I don't *want* multiple third-party products to register this adapter:
I think it belongs to the integrator to set the policy for the site.
"Reusable policy" is an oxymoron.


Tres.
- --
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Tres Seaver          +1 540-429-0999          tseaver at palladion.com
Palladion Software   "Excellence by Design"    http://palladion.com
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