Contao - Inserttag for counting entries.

config.php

<?php
// config.php
$GLOBALS['TL_HOOKS']['replaceInsertTags'][] = array('ExtendedComments', 'myReplaceInsertTags');

class ExtendedComments
{
	/**
	 * Replace a inserttag.
	 *
	 * @param $strTag The inserttag.
	 *
	 * @return bool|mixed|null The value or false on error or unknown inserttag.
	 */
	public function myReplaceInsertTags($strTag)
	{
		$arrParts = trimsplit('::', $strTag);

		if ($arrParts[0] == 'comments')
		{
			return $this->countComments($arrParts[1], $arrParts[2]);
		}

		return false;
	}

	/**
	 * Get the count for comments.
	 *
	 * @param string $strParentTable Name of parent e.g. tl_news.
	 *
	 * @param int    $intParentId    Id of the parent.
	 *
	 * @return bool|mixed|null The count value or false on error or null if empty.
	 */
	protected function countComments($strParentTable, $intParentId)
	{
		if (empty($strParentTable) || empty($intParentId))
		{
			return false;
		}

		$objResult = \Database::getInstance()
			->prepare('SELECT COUNT(*) as mycount FROM tl_comments WHERE source=? AND parent=?')
			->execute($strParentTable, $intParentId);

		return $objResult->mycount;
	}
}