[Zope3-dev] EventService, references, and subscription semantics

[Steve Alexander]

Steve Alexander wrote:
> Shane Hathaway wrote:
> 
>>
>> Well, I may be wrong, but I don't think you can go that far.  If you 
>> have a persistent LDAP-backed user database and you want to register 
>> an LDAP-based user object as an event listener (perhaps to expire the 
>> user's password), how would the IReferenceLookup utility know to use a 
>> path/userid-based reference as opposed to a persistence-based 
>> reference or an LDAP-based reference?  The only interface of the user 
>> objects is IPrincipal.
> 
> 
> So, you configure your IReferenceLookup utility to make decisions based 
> on the location/context of the object.
> 
> Or, you make your Principals implement ILDAPLookedUp (in addition to 
> IPrincipal), which the IReferenceLookup is configured to know about.

In fact, I think a neat answer would be for the IReferenceLookup to grab 
an IReferenceLookupImplementation from the context of the object we want 
an IReference for.

So, an object's context is responsible for providing a utility to say 
how to make an appropriate kind of reference.

       Root  :-- IReferenceLookup (service)
      /    \
     Bar   Foo
    /        \
  Baz        LDAPUserFolder   :-- IReferenceLookupUtility
                \
                 LDAP Principal Object


So, object Baz gets the LDAP Principal Object (let's call it "user"). It 
wants to store a reference to user:

   1: Baz gets the IReferenceLookup service

   2: Baz passes user to the IReferenceLookup service

   3: The service examines user's context wrapper, and walks the wrapper
      looking for an IReferenceLookupUtility

   4; The service passes user to the IReferenceLookupUtility, which
      returns an appropriate IReference object


Your LDAPUserFolder would be equipped with the nous to get for objects 
in its context the appropriate kind of IReference.

The IReferenceLookup service could have sensible defaults (configured in 
zcml), for when no IReferenceLookupUtility could be found, or when it 
doesn't know what to do.

--
Steve Alexander