DataMapper ORM v1.8.0

[eluser]WanWizard[/eluser]
@Chillahan,

In Datamapper, the column 'id' is required, MUST be called 'id', and must be an integer auto increment primary key. There is no way around it, the column name is hardcoded everywhere, and not easy to change (as you have noticed). This is on the roadmap though, probably for v2.0.

I'm not in favour for it though, it is against database design best practices to use data columns for primary keys, altough that's what you've been tought in school when dicussion normalisation.
If you use data columns, that means you hardcode the structure of your database into your application. Also, when you change the database stucture, you might have a migration nightmare on your hands as foreign keys might change,
You solve that by using an abstract field as primary key.

To answer your questions:
1) The field $row->id doesn't exist, you'll get a notice, and the value defaults to FALSE. $this->id != FALSE is TRUE, so the method it doesn't return FALSE.
2) You can't.
3) Datamapper uses the CI database library's transaction methods, to wrap it's operations in. This means you can not use DM transactions over multiple database operations. Use $this->db->trans...() instead to wrap it around multiple DM operations.
(some db engines, like MySQL, don't allow you to nest transactions. Starting a transaction will immediately commit the previous one).

As for the inconsistency:

If you create a new object, and you do $objectA->save($objectB), it will immediately add the ITFK to objectA if the relation is so that there is a one-to-many from A to B. However, if you just do $objectA->save(), there is obviously no relation to save, and the ITFK is set to NULL.