Valid array gives php Invalid argument supplied for foreach() - php

Question

I have the following foreach loop that gives me the invalid argument error:
$all_students = $this -> model_accounts -> get_students_on_account($account['account_id']);
foreach ($all_students as $student)
{
...
}
I tried to debug using print_r to check what the $all_students array looks like and I got this as a result:
Array
(
[0] => Array
(
[id] => 00062
[student_name] => Reckless
[student_surname] => Harmse
[acc_id] => 198
[dob] => 07-07-1993
[gender] => Male
[active] => 1
[has_pic] => 1
[avatar] => 106.jpg
[pic_ver] => 1
[student_identity_num] => 9307075052084
)
)
So the array is there and as seen in the print_r details, it is seen as an array.
I have looked at other similar questions and none of them could help.
Thanx in advance
Added:
Model function used to get the students
function get_students_on_account($account_id)
{
$data = '';
$this->db->where('acc_id', $account_id);
$q = $this->db->get('students');
if ($q->num_rows() > 0)
{
foreach ($q->result_array() as $row)
{
$row['dob'] = $this -> change_date_format($row['dob']);
$data[] = $row;
}
}
return $data;
}

Answer 1

In your function get_students_on_account, replace this:
$data = '';
by this:
$data = array();
This is needed to consistently return an array. You don't want to return a string. When it does, the problem that you described will occur.

Answer 2

Try this
$res = $q->result_array();
foreach ($res as &$row)
{
$row['dob'] = $this -> change_date_format($row['dob']);
}
return $res;

Answer 3

Try this
In Controller
$all_students = $this->model_accounts->get_students_on_account($account['account_id']);
if($all_students == false){
echo "Empty result";
}
else{
foreach ($all_students[0] as $student)
{
...
}
}
In Model
function get_students_on_account($account_id)
{
$query = $this->db->query("SELECT * FROM students WHERE acc_id = $account_id");
$result = $query->result_array();
$count = count($result);
if (empty($count)) {
return false;
}
else{
return $result;
}
}