Tools\Model\Table\Table::getFieldInUse PHP Method

    public function getFieldInUse($groupField, $type = 'all', array $options = [])
    {
        $defaults = ['group' => $groupField, 'order' => [$this->displayField() => 'ASC']];
        if ($type === 'list') {
            $defaults['fields'] = ['' . $this->primaryKey(), '' . $this->displayField()];
        }
        $options += $defaults;
        return $this->find($type, $options);
    }