[Zope3-Users] Multiple containers in one object - how to implement in Zope3?

[Jeff Rush]

Alek Kowalczyk wrote:
> Florian Lindner napisał(a):
> 
>>Am Samstag, 1. April 2006 15:15 schrieb Alek Kowalczyk:
>>  
>>>I have a single object, which can contain many objects of 2 another
>>>types (IType1, IType2). My intention is to have those objects contained
>>>in separate collections (because they are very different 2 types of
>>>objects and should not be mixed in one collection)
>>>I'd like to have each collection editable like Zope folder, i.e each
>>>collection to be IContainer/BTreeContainer.

>>why don't just create two subfolders (of type zope.folder) in you Container 
>>object, one for IType1, one for IType2?
>>
> Good idea, thanks! In the meantime I have made something similar, i.e 
> defined two more container types (IObjects1, IObjects2) and created one 
> IObjects1 and one IObjects2 in the IMasterObject's (which now is also a 
> IContainer) constructor .
> 
> But now the new question follows:  how to limit cardinality of items? I 
> want now to have one and exactly one IObjects1 and IObjects2 instance in 
> IMasterObject. Is there some type of constraint defined, similar to 
> ItemTypeConstraint, for limiting number of elements of specific type, or 
> I should do it on my own by overriding __setitem__ and other methods?

Alek, I do the same thing for a complex container with a fixed set of member 
sub-containers.

   IVenture("RUSH")
     ILedgerSet, name "ledgers"
        ILedgers
        ...
     IJournalSet, name "journals"
        IJournals
        ...

   http://sample.com/ventures/RUSH/ledgers/CASH
   http://sample.com/ventures/RUSH/journals/CHECKING

The way to get what you want is to make IMasterObject *not* an IContainer 
but an IReadContainer.

There are IWriteContainer and IReadContainer which are sub-interfaces of 
IContainer.

This way no one can ever add/remove those sub-containers.  And (presumeably 
you're doing it now) you add those the instances of Objects1 and Objects2 at 
creation time of MasterObject, and then never again need to manipulate them.

You should also place Container/Containee constraints on the IObjects1 and 
IObjects2 so they cannot be created in inappropriate places, and of course 
omit their menu entries from the ZMI so they are not manually addable.

-Jeff