How to append a serialized string that already exists in the database - php

Question

I have just started to learn about serialization and I have a question that I cannot seem to find a simple explanation to.
Say I had a table called week and inside week I had 3 columns with the third column containing a bunch of serialized meal IDs like so stored in my database:
INSERT INTO `week` (`week_id`, `meal_code`, `meal_id`) VALUES
(1, 'week12016', 'a:6:{i:0;i:1;i:1;i:2;i:2;i:3;i:3;i:4;i:4;i:5;i:5;i:6;}');
But later I want to append another meal_id to the existing string but not update any other column so it reads
(1, 'week12016','a:7:{i:0;i:1;i:1;i:2;i:2;i:3;i:3;i:4;i:4;i:5;i:5;i:6;i:6;i:7;}')
I have tried in a php file to store the following
$food=array("7");
$sfood=serialize($food);
Then trying to add the 7 to the existing meal_ids in the week table
mysqli_query($conn,"UPDATE week
SET meal_id ('$sfood')");
//if entry into the database is successful, confirm with a alert popup and refresh the home page
if(mysqli_affected_rows($conn) > 0){
//header("location: admin.php");
header("refresh:0; url=admin.php");
echo "<script type='text/javascript'>alert('Upload Successful!')</script>";
exit;
But when I check my database, nothing has changed.
What am I doing wrong, is it even possible to do what I am trying to achieve?

Answer 1

You have to read the column from your table row. Unserialize it into a PHP variable and then add a new occurance to it.
Then serialize the new array and store it back to your database
// SELECT from table
$s = 'a:7:{i:0;i:1;i:1;i:2;i:2;i:3;i:3;i:4;i:4;i:5;i:5;i:6;i:6;i:7;}';
$d = unserialize($s);
print_r($d);
$d[] = 99;
print_r($d);
$s2 = serialize($d);
echo $s2;
// UPDATE table row
RESULTS
Array
(
[0] => 1
[1] => 2
[2] => 3
[3] => 4
[4] => 5
[5] => 6
[6] => 7
)
Array
(
[0] => 1
[1] => 2
[2] => 3
[3] => 4
[4] => 5
[5] => 6
[6] => 7
[7] => 99
)
a:8:{i:0;i:1;i:1;i:2;i:2;i:3;i:3;i:4;i:4;i:5;i:5;i:6;i:6;i:7;i:7;i:99;}
Storing data like this is not recommended, as it makes this data impossible to process using queries