Ah sorry about not responding to this earlier.

I needed to register an activity entity association for content comments and discussion messages so they end up in the correct content or discussion stream. Since that is based on the objectType I needed either 2 distinct object types or register the association in oae-messagebox and do something like:

```javascript
ActivityAPI.registerActivityEntityAssociation('comment', 'self', function(associationsCtx, entity, callback) {
    if (entity.contentId) {
        return callback(null, [entity.contentId]);
    } else if (entity.discussionId) {
        return callback(null, [entity.discussionId]); 
    }
});
```

I opted to have 2 separate ones and keep them in their respective modules.