There's a subtle difference between the standard AdapterRegistry (from zope.interface.adapter) used for the global component registry and PersistentAdapterRegistry (from zope.component.persistentregistry) -- apart from the fact that the latter is persistent:

When you set the __bases__ property on AdapterRegistry, it tells the adapter registries higher up in the hierarchy that it's there by calling an _addSubregistry() method on them, PersistentAdapterRegistry doesn't do this and doesn't have an _addSubregistry() method.



Usually this doesn't come into effect because the global component registry with a regular AdapterRegistry is typically highest in the hierarchy:

             global component registry
                w/ AdapterRegistry
                         ^
                         |
                         |
  persistent component registry (e.g. ++etc++site)
          w/ PersistentAdapterRegistry
                         ^
                         |
                         |
  persistent component registry (e.g. ++etc++site)
          w/ PersistentAdapterRegistry
                         |
                        ...


Now, let's imagine you actually put a "global" (that means non- persistent) component registry *after* a persistent component registry, e.g. you have

                 global component registry
                    w/ AdapterRegistry
                             ^
                             |
                             |
        persistent component registry (e.g. ++etc++site)
                w/ PersistentAdapterRegistry
                             ^
                             |
                             |
non-persistent component registry (created during traversal)
                     w/ AdapterRegistry


Creating that non-persistent component registry works fine, you can simply use BaseGlobalComponents(). However, when you set the __bases__, AdapterRegistry will try to call _addSubregistry() on the PersistentAdapterRegistry that's higher up in the hierarchy and the whole thing goes ka-boom:

Traceback (most recent call last):
  ...
File "/Users/philipp/dev/ploneout/src/kss.core/kss/core/ azaxview.py", line 60, in __init__
    self._sitemanager.__bases__ = (next, )
  ...
AttributeError: 'PersistentAdapterRegistry' object has no attribute '_addSubregistry'


This is quite annoying. Do I have to write my own component registry, subclassign from BaseGlobalComponents so that I won't use AdapterRegistry but a variant that doesn't end up assuming _addSubregistry on the other registries? Or is the _addSubregistry thign some legacy that can be removed (it doesn't seem to be used at all in Zope 3 currently)?

Philipp


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