[Zope-CMF] Extending FTI.isConstructionAllowed

[Wichert Akkerman]

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.

Wichert.

-- 
Wichert Akkerman <wichert at wiggy.net>    It is simple to make things.
http://www.wiggy.net/                   It is hard to make things simple.