Re: How to remove an object and all its references ?

On Fri, Aug 12, 2016 at 1:30 AM, <[email protected]> wrote:

> Good morning,
>
> I'm quite new to ZODB and I wonder if there is a way to remove a stored
> object with all its references ?
> persistent weak ref seems a nice path, but objects are collected on pack
> operation only IIUC.
>
> What I'd like to do : create a persistent object, store it into the
> database and add it to a BTree. When I delete the original object stored in
> database, I'd like it removed from BTree too.
>
> If there is such a way, do I have to care about performance impact for
> collecting and removing all references ?
>

There are two levels at which to think about this question.

In this context, you should think about ZODB as persistent memory in a
high-level language.  As with Python, objects are removed through garbage
collection. There's no way to explicitly deallocate/remove objects.

At the application level, as with Python, you could arrange automation to
remove objects from collections, often some sort of master collection and
secondary collections (e.g. index).  How this is done seems to depend a lot
of application requirements and tradeoffs. As a result, there's more than
one way to do it.

A very common pattern in the Zope community (including Plone, etc.) is to
use a "catalog" which is a collection of objects with indexes.  When object
lifecycle events happen, methods are called on the catalog to add, update,
or remove objects. Because Zope was designed to be wildly extensible, a
number of abstractions (base classes, event systems, special methods) are
used to automate this, which leads to some complexity.  I haven't used
Zope-based catalog machinery in a while, so I can't point to the current
best examples.

Less ambitious applications can use simpler frameworks to do the same thing.



> Thanks for your help.
>

I hope I was helpful.

Jim

-- 
Jim Fulton
http://jimfulton.info

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