How to update data in database with CodeIgniter? - codeigniter

Question

When I update the data in the database using the form below, the error following error is shown. How can I solve this error?
Cannot add or update a child row: a foreign key constraint fails
(`nov-cms`.`faqs_cat`, CONSTRAINT `faqs_cat_ibfk_20` FOREIGN KEY (`id`)
REFERENCES `tblfaqs` (`id`) ON DELETE CASCADE ON UPDATE CASCADE)'
Form:
function editpage_($editid) {
$conn = Doctrine_Manager::connection();
$data['headingtop'] = "FAQ'S > FAQ'S > Edit FAQ'S";
$data['title_faqs'] = "Edit FAQ's";
$data['errormess'] = '';
$title_faqs = addslashes($this->input->post('title_faqs'));
$content = addslashes($this->input->post('editor1'));
$seo_description = addslashes($this->input->post('seo_description'));
$category = $this->input->post('category'); //print_r($category['cate']); exit;
$isActive = $this->input->post('isactive');
$position = $this->input->post('position');
$qryDel2 = $conn->prepare("DELETE from faqs_cat where id='$editid'");
$qryDel2->execute();
$query = $conn->prepare("UPDATE tblfaqs SET title_faqs='$title_faqs',content='$content',isActive='$isActive',position='$position',seo_description='$seo_description' WHERE id='$editid' ");
$query->execute();
$id = $conn->lastInsertId();
//when we add a page this insert a record to table, and this is id of record inserted.. this is a function default of mysql, we use to get last insert id to insert this to orther table...
foreach ($category as $data) {
$query = $conn->prepare("insert into faqs_cat (fc_id, id, category_id) values ('','$id','$data')"); //in this.
$query->execute();
}
$url = 'admin/faqs/';
echo'
<script>
window.location.href = "' . base_url() . $url . '";
</script>
';

Answer 1

The error is in this line:
$id = $conn->lastInsertId();
Specifically, $id remains empty because lastInsertId() is not returning a value. This causes the constraint to fail because when inserting into faqs_cat an ID is required.
If you're trying to get an auto-generated key from the database, you may need to specify a sequence name to lastInsertId depending on what type of database you're connecting to (for example, Postgres requires a sequence name). Try creating a sequence called 'mySequence' and using this instead:
$id = $conn->lastInsertId('mySequence');