Missing capability to do views relationships with Fields? Missing 'views data' op?

@yched, thanks so much for the detailed answer. I'm still a bit adrift, and hope you can bear with me for a bit more:

You say:

Same principle as in D6 : your hook implementation can either grab 'sensible default data' provided by field_views_field_default_views_data($field) and build from there (highly recommended), or start from scratch and build the whole array of views data on its own.

So you're saying that I can implement hook_views_data_alter() in my module and alter the views data to add relationships? That makes sense, but as a practical matter, my module has no idea which of the items in the $data might be its own. Field module knows, that, but my module doesn't.

I've implemented hook_views_data_alter() in my module per dereine's suggestion in IRC, but can't see how to select out of $data what would belong to my module. Is it possible to do so?

Thanks again,
-Randy

Thanks for the continuing help. Implementing hook_field_views_data() is going to be the ticket, I think. You probably said that before, but you know how it goes.

So a couple of questions:
I'm going to copy field_views_field_default_views_data() in asin_field_views_data().

I notice in field_views_field_default_views_data() this note:

  // Note: this should be in the $field object already, see http://drupal.org/node/645926.
  $field_storage_details = field_sql_storage_field_storage_details($field, NULL);
  $field += $field_storage_details;

That issue did land. Should we be pulling this out?

Second, in field_views_data() we have

    $module = $field['module'];
    $result = (array) module_invoke($module, 'field_views_data', $field);
    drupal_alter('field_views_data', $result, $field);

    if (empty($result)) {
      $result = field_views_field_default_views_data($field);
    }

The drupal_alter() comes after the module_invoke(). Wouldn't it be more useful after the defaults are loaded? In fact, it would probably be better for my module to do an asin_field_views_data_alter() than to replicate the entire default data.

My code is WORKING! Thanks so much for the help.

Related issues per #4 above:
#761754: Removed outdated storage details in field_views_field_default_views_data()
#761758: Move drupal_alter() for hook_field_views_data_alter() to more useful spot

If anybody else needs to implement relationships like this, the resulting code will be in Amazon module, asin/asin.module, in asin_field_views_data().

Pretty amazing community support.
yched++
dereine++

I added a minor paragraph about this in the CCK to Fields update page hook_field_settings() section. It can be better. Maybe when I have the actual code boiled down better I'll improve it.

Thanks, yched, I did understand that.

But I did actually start by copying the code. And I haven't finished doing it right. It's not obvious what the correct approach is to alter or to build from what field_views_field_default_views_data() does.

If all I want to do is add a relationship, and I called

$data = field_views_field_default_views_data();
... do the right thing here to add a relationship ...

What would the right thing be?
What I did in the copied code was:

foreach ($tables as $table) {

...

      // Add a relationship for related node.
      $data[$table][$column_real_name]['relationship'] = array(
        'base' => 'amazon_item',
        'field' => $column_real_name,
        'handler' => 'views_handler_relationship',
      );
}

So it looks like the work remaining is to get $column_real_name, and that's about it, right?

But then $tables is not exactly equivalent to $data.