add this to save action
if (isset($data['categories'])) {
$data['categories'] = explode(',', $data['categories']);
if (is_array($data['categories'])) {
$data['categories'] = array_unique($data['categories']);
}
}
and this to collection
$this->getSelect()->join(
array('category_table' => $this->getTable('qbanner/qbanner_category')), 'main_table.qbanner_id = category_table.qbanner_id', array()
)
->where('category_table.category_id = ?', $categoryId);
return $this;
hope this will help you