plone.uuid

This is a minimal package that can be used to obtain a universally unique identifier (UUID) for an object.

The default implementation uses the Python standard library uuid module to generate an RFC 4122-compliant UUID, using the uuid4() function. It will assign a UUID upon object creation (by subscribing to IObjectCreatedEvent from zope.lifecycleevent) and store it in an attribute on the object.

Why use an attribute and not annotations? The most common form of annotation is the one provided by IAttributeAnnotations. This stores annotations in a BTree in an attribute called __annotations__, which means that annotation values do not end up in the same ZODB persistent object as the parent. This is good for "large" values, but not very good for small ones that are frequently required, as it requires a separate ZODB object load.

Simple usage

To automatically assign a UUID to your objects using the default implementation outlined above, you should:

• Make sure they implement plone.uuid.interfaces.IAttributeUUID. You can do this in code, via the implements() directive, or in ZCML, with a statement like:

  <class class="my.package.MyClass">
      <implements interface="plone.uuid.interfaces.IAttributeUUID" />
  </class>
  

• Make sure that an IObjectCreatedEvent is fired for this object when it is first created.

Once the event handler has triggered, you can obtain a UUID by adapting the object to the IUUID interface:

from plone.uuid.interfaces import IUUID
uuid = IUUID(context)

The uuid variable will now be a (byte) string containing a UUID. If the UUID has not yet been assigned, adaptation will fail with a TypeError.

If you would rather get None instead of a TypeError, you can do:

uuid = IUUID(context, None)

UUID view

If you require a UUID in a page template or remotely, you can use the @@uuid view, which is registered for all objects that provide the IUUIDAware marker interface (which is a super-interface of the IAttributeUUID marker seen above).

For example:

<div tal:attributes="id string:uuid-${context/@@uuid}">
    ...
</div>

The view simply returns the UUID string as looked up by the IUUID adapter.

Customising behaviour

There are two primary customisation points for this package:

• You can change the default UUID generating algorithm by overriding the unnamed utility providing the IUUIDGenerator interface. The default implementation simply calls uuid.uuid4() and casts the result to a str.

• You can change the UUID storage by providing a custom IUUID adapter implementation. If you do this, you must also provide a mechanism for assigning UUIDs upon object creation, usually via an event handler. To obtain a UUID, use the IUUIDGenerator interface:

  from zope.component import getUtility
  from plone.uuid.interfaces import IUUIDGenerator
  
  generator = getUtility(IUUIDGenerator)
  uuid = generator()
  

  You should also make sure that instances with a UUID provide a sub-interface of plone.uuid.interfaces.IUUIDAware.