Pull Request for Issue #21867.

Summary of Changes

to make joomla's admin model aware of subforms so you can actually handle them in seperate tables with their corresponding model

Testing Instructions

use a subform to add a row

Expected result

some DB-table has a row added which is handled by default CMS functions

Actual result

the row gets stashed away in a json field making it unpractical for sorting, searching, ACL, and just about anything

Documentation Changes Required

tbd

Example usage

Instead of extending \Joomla\CMS\MVC\ModelAdminModel ; extend this class to have your form handle subforms with their own respective models and forms

Off course you'll need to provide the model and form you want your subform to use. So in the example below you'd provide:

/**
 * Model for a list of History items
 *
 * @since 0.0.1
 */
class AmberModelHistories extends ListModel
{
// as you would when creating a listview like normal 
}

snippet from example form .xml:

<field
	name="histories"
	type="subform"
	formsource="/administrator/components/com_amber/models/forms/histories.xml"
	multiple="true"
	layout="joomla.form.field.subform.repeatable-table"
	/>

content of histories.xml:
note the fieldgroup name which needs to match the name of the subform

<?xml version="1.0" encoding="utf-8"?>
<form>
<fieldgroup name="histories">
		<field
				name="historyID"
				type="hidden"
				/>
		<field
				name="resourceID"
				type="resource"
				label="COM_AMBER_RESOURCE_TITLE_LABEL"
				description="COM_AMBER_RESOURCE_TITLE_DESC"
				class="inputbox"
				/>
		<field
				name="difQty"
				type="number"
				label="COM_AMBER_QUANTITY_LABEL"
				description="COM_AMBER_QUANTITY_DESC"
				class="inputbox"
				/>
</fieldgroup>
				
</form>

the controller for the subform:
/administrator/compontents/com_amber/controllers/histories.php

class AmberControllerHistories extends AdminController
{

	public function getModel($name = 'History', $prefix = 'AmberModel', $config = array('ignore_request' => true))
	{
		$model = parent::getModel($name, $prefix, $config);
                return $model;
	}