update checkboxes after submit - php

Question

I am currently running into an issue, where I have this form consisting of checkboxes. I get the values of user preferences for the checkboxes from a database. Everything works great, and does what is supposed to do, however after I change and check some boxes and then hit the submit button, it will still show the old values to the form again. If I click again in the page again it will show the new values.
The code is shown below with comments.
<form action="myprofile.php" method="post">
<?php $usr_cats=array();
$qry_usrcat="SELECT category_id_fk
FROM user_categories
WHERE user_id_fk='".$_SESSION['user_id']."';";
$result = mysqli_query($conn,$qry_usrcat);
while($row = mysqli_fetch_array($result)){
$usr_cats[] = $row[0]; // getting user categories from db stored in array
}
$query_allcats="SELECT category_id,category_name, portal_name
FROM categories
INNER JOIN portals on categories.portal_id=portals.portal_id
ORDER BY category_id;"; // select all category queries
$result = mysqli_query($conn,$query_allcats);
while($row = mysqli_fetch_array($result)){
echo $row['portal_name'] . "<input "; //print categories
if(in_array($row['category_id'], $usr_cats)){ // if in array from db, check the checkbox
echo "checked ";
}
echo "type='checkbox' name='categories[]' value='";
echo $row['category_id']."'> ". $row['category_name']."</br>\n\t\t\t\t\t\t";
}
?>
<input type="submit" name="submit" value="Submit"/>
<?php
$qry_del_usrcats="DELETE FROM user_categories
WHERE user_id_fk='".$_SESSION['user_id']."';"; //delete all query
if(isset($_POST['submit'])){
if(!empty($_POST['categories'])){
$cats= $_POST['categories'];
$result = mysqli_query($conn,$qry_del_usrcats); //delete all
for ($x = 0; $x < count($cats); $x++) {
$qry_add_usrcats="INSERT INTO `user_categories` (`user_id_fk`, `category_id_fk`)
VALUES ('".$_SESSION['user_id']."', '".$cats[$x]."');";
$result = mysqli_query($conn,$qry_add_usrcats);
}
echo "success";
}
elseif(empty($_POST['categories'])){ //if nothing is selected delete all
$result = mysqli_query($conn,$qry_del_usrcats);
}
unset($usr_cats);
unset($cats);
}
?>
I am not sure what is causing to do that. Something is causing not to update the form after the submission. However, as i said everything works great meaning after i submit the values are stored and saved in the DB, but not shown/updated on the form. Let me know if you need any clarifications.
Thank you

Answer 1

Your procedural logic is backwards and you're doing a bunch of INSERT queries you don't need. As #sean said, change the order.
<?php
if(isset($_POST['submit'])){
if(isset($_POST['categories'])){
$cats= $_POST['categories'];
// don't do an INSERT for each category, build the values and do only one INSERT query with multiple values
$values = '';
for($x = 0; $x < count($cats); $x++) {
// add each value...
$values .= "('".$_SESSION['user_id']."', '".$cats[$x]."'),";
}
// trim the trailing apostrophe and add the values to the query
$qry_add_usrcats="INSERT INTO `user_categories` (`user_id_fk`, `category_id_fk`) VALUES ". rtrim($values,',');
$result = mysqli_query($conn,$qry_add_usrcats);
echo "success";
}
elseif(!isset($_POST['categories'])){ //if nothing is selected delete all
// you may want to put this query first, so if something is checked you delete all, so the db is clean and ready for the new data.
// and if nothing is checked, you're still deleting....
$qry_del_usrcats="DELETE FROM user_categories WHERE user_id_fk='".$_SESSION['user_id']."';"; //delete all query
$result = mysqli_query($conn,$qry_del_usrcats);
}
unset($usr_cats);
unset($cats);
}
?>
<form action="myprofile.php" method="post">
<?php $usr_cats=array();
$qry_usrcat="SELECT category_id_fk FROM user_categories WHERE user_id_fk='".$_SESSION['user_id']."';";
$result = mysqli_query($conn,$qry_usrcat);
while($row = mysqli_fetch_array($result)){
$usr_cats[] = $row[0]; // getting user categories from db stored in array
}
$query_allcats="SELECT category_id,category_name, portal_name FROM categories INNER JOIN portals on categories.portal_id=portals.portal_id ORDER BY category_id;"; // select all category queries
$result = mysqli_query($conn,$query_allcats);
while($row = mysqli_fetch_array($result)){
echo $row['portal_name'] . "<input "; //print categories
if(in_array($row['category_id'], $usr_cats)){ // if in array from db, check the checkbox
echo "checked ";
}
echo "type='checkbox' name='categories[]' value='";
echo $row['category_id']."'> ". $row['category_name']."</br>\n\t\t\t\t\t\t";
}
?>
<input type="submit" name="submit" value="Submit"/>

Answer 2

Typically this occurs due to the order of your queries within the script.
If you want to show your updated results after submission, you should make your update or insert queries to be conditional, and have the script call itself. The order of your scripts is fine, but you just need to do the following:
Take this query:
$qry_del_usrcats="DELETE FROM user_categories
WHERE user_id_fk='".$_SESSION['user_id']."';"
and put it inside the if statement so it looks like this:
if (isset($_POST['submit'] {
$qry_del_usrcats="DELETE FROM user_categories
WHERE user_id_fk='".$_SESSION['user_id']."';"
$result = mysqli_query($conn,$qry_del_usrcats);
[along with the other updates you have]
}
Also, you will need to move this entire conditional above the form itself; typically any updates, inserts, or deletes should appear year the top of the form, and then call the selects afterward (outside of the conditional)