CodeIgniter session shows different output in different functions - codeigniter

Question

In first function of my controller, I am fetching random records from mysql table using CI active record
$query = $this->db->query("SELECT DISTINCT * FROM questions WHERE `level` = '1' ORDER BY RAND() limit 0,5");
$result = $query->result_array();
and saving result in session as
// saving questions id in session
for($i = 0; $i < count($result); $i++)
{
$session['questionsId'][] = $result[$i]['qId'];
}
$this->session->set_userdata($session);
and if print session variable it shows output like:
$qIds_o = $this->session->userdata('questionsId');
var_debug($qIds_o);
Array
(
[0] => 5
[1] => 9
[2] => 3
[3] => 6
[4] => 11
)
but if I retrieve same session in another function of same controller it shows different result
$qIds = $this->session->userdata('questionsId');
var_debug($qIds);
Array
(
[0] => 2
[1] => 8
[2] => 6
[3] => 3
[4] => 5
)
and if I remove ORDER BY RAND() from mysql query like:
$this->db->query("SELECT DISTINCT * FROM questions WHERE `level` = '1' limit 0,5");
it shows same session array in both functions. Very strange.
Please guide what is going wrong....
Here is my controller script:
public function set_value(){
$query = $this->db->query("SELECT DISTINCT * FROM questions WHERE `level` = '1' ORDER BY RAND() limit 0,5");
$result = $query->result_array();
// saving questions id in session
for($i = 0; $i < count($result); $i++)
{
$session['questionsId'][] = $result[$i]['qId'];
}
$this->session->set_userdata($session);
$qIds_o = $this->session->userdata('questionsId');
var_debug($qIds_o);
}
public function get_value(){
$qIds = $this->session->userdata('questionsId');
var_debug($qIds);
}
I called set_value() on page load while once the page loaded I call get_value() using AJAX post which simply hits my_controller/get_value/ and response back to browser.

Answer 1

Without looking at your controller (let's call it my_controller in detail, I think what might be happening is:
(1) You call the first function, my_controller/set_value where set_value sets the session variable and you echo the result.
(2) You then call the second function, show_value that simply echos out the session variable.
What you might be doing in set_value is:
1) echo out the current session variable
2) call the query and re-set the session variable
If this is the case, then when you go to show_value (2nd function) you are looking at the recently re-set value instead of the prior value that you echoed out in the first function.

Answer 2

I have two questions about this sentence:
but if I retrieve same session in another function of same controller it shows different result
Is this on a new page load?
If so, is the query run again?
I'm going to assume the answer to both of these questions is yes, since you said removing RAND() gives you the same results.
You are using a combination of RAND() and LIMIT in your query, meaning you want only five rows in a random order. That means that each time the query is run (and your session data is set), it is very likely that the results will be different.
I don't know exactly what you're doing with these IDs and what sort of data set you need, so this may not be 100% perfect for your solution, but if you only need to set this session data once, you should check if it exists before running the query.
if ($this->session->userdata('questionsId') === FALSE)
{
// Run your query and set your session data here.
// Note that in CI 3.0, Session::userdata()
// will return NULL if empty, not a boolean.
}