Universal entity id?

Sounds like you want a UUID. :)

.. or just a generic $entity->id to go along with the equally generic $entity->type? Or be verbose if you must by having $entity->entity_type and $entity->entity_id.

You can always reliably get the ID using entity_extract_ids().

I think we want to add an easy id accessor to our entity class, e.g. $entity->identifier() . As done in #1184944: Make entities classed objects, introduce CRUD support. Maybe the shorther $entity->id() would b even better?

This type of problem has come up for me a few times too. Maybe the fruits of entity_extract_ids work should always be present when entities are loaded, and integrated in somehow.

We should consider enforcing id as the actual key - if you don't use it as a column name (or have entities that don't exist in the db) it could still be handled by the controller, would save adding the getter. Either way would be preferable to entity_extract_ids() though.

This is what I made out of it: http://drupal.org/project/entity_index

>We should consider enforcing id as the actual key - if you don't use it as a column name (or have entities that don't exist in the db) it could still be handled by the controller, would save adding the getter.

I like that idea, however wouldn't it mean there is no $node->nid any more?

The work being done over at Proposing a 2.x branch (generic entity solution) [for UUID] is relevant here.

#1637370: Add UUID support to core entity types