Missing Documentation: Model Service - $_hook_id

[RK311y]

Suggested Change

The Model Service documentation is missing a description of the $_hook_id property. The example I have found that uses this property is within the Member Model.

Reasoning

I was developing an add-on that contains a Contact model which belongsTo the ee:Member model.
Being curious in the process in which member models are saved/updated/inserted/deleted, I went searching for the extension hook call before_member_save($member, $values).

Based on the documentation, I was lead to believe that all extension hooks are invoked via some code that looks like:

if (ee()->extensions->active_hook('some_hook_method') === TRUE)
{
    $str = ee()->extensions->call('some_hook_method', $hook_args...);
}

Unable to locate the existence of such code, with the hook method before_member_save, I did some deeper digging.

I learned that Models, which extend the ExpressionEngine\Service\Model class invoke the forwardEventToHooks($event) method. Walking through the code of this method, I discovered that:

1. Models which have a $_hook_id property defined are exposed to extension hook calls (Event name, either 'insert', 'update', 'save', or 'delete') based on the following convention:

$forwarded = array(
    'before' . $uc_first_event => 'before_' . $hook_basename . '_' . $event,
    'after' . $uc_first_event => 'after_' . $hook_basename . '_' . $event
);

2. Internal events on the Model are also emitted without having to call them externally: For example:

$model = ee('Model')->get('Member')->first();
$model->validate(); // internally, $this->emit('beforeValidate') and $this->emit('afterValidate') are called
$model->save(); // internally, $this->emit('beforeSave') and $this->emit('afterSave') are called
// .... etc

Before I was attaching my own events for these actions and having to emit (invoke) them manually.

Additional context

I would recommend adding this documentation here: Building your own Models