Create relation field

Why has this not been done anywhere yet? It seems like such a core piece of functionality to the relation module. I was about to code my own field for a system I'm building and then I found this... but I'm hesitant to use the "relation add" module which is centered around a "block". Is this a departure from the purpose of the module? Does anyone have advice for me of other discussions / attempts that have been made around this desired functionality?

Actually, it seems like this functionality exists in: http://drupal.org/project/relation_select. Care to comment on differences?

The main advantages of relation add module:
- uses a different widget which is less problematic and more node reference like
- it lets you fully use the fieldable relations, cause you can fill the additional fields when you create the connection, relation select does not have this functionality.

Great module! Thanks a lot!

The dropdown for the releation type isn't set when editing a node. On line 527 it should be
'#default_value' => isset($type) ? $type : NULL,

it would be nice to store the resulting relation ids with the field, so one can use the delta to change the weight. do you accept patches?

I've got some fixes for special cases here: I have directional relations on the same node type and restrict the field only to those relations. This patch fixes the relation_type_load call for reversed releations and replaces the reverse relation detection by looking at the endpoint data.

This patch is looking great!

The only issue I ran into is when two content types share the same directional relation field, one with a reverse endpoint - when a relation is deleted from one field instance, it still appears in the other, until a cache clear.

Quick proof of concept (not a patch, but I can add one if this seems reasonable):
In function relation_add_field_update():

foreach ($items as $key => $item) {
    if (isset($item['delete']) && $item['delete']) {
      if (isset($item['relation_options']['rid']) && $item['relation_options']['rid']) {
        relation_delete($item['relation_options']['rid']);
+        cache_clear_all('field', 'cache_field', TRUE);
      }
      continue;
    }

It would probalby be better to target the individual field cache directly - something like what relation_add_entity_presave() does, but checking each bundle the field may be part of…

Ok patch and interdiff attached.

@mr.york #15 is a confusing response given your patch in #12.

In any case, should I open #13/14 as a separate issue?