php var_dump shows array but can't access it - php

Question

Can't access array but var_dump() sees it.
session_start();
include './entities/Answer.php';
include './entities/Question.php';
include './Database.php';
if (isset($_SESSION["question"])) {
$correct = TRUE;
var_dump($_SESSION["question"]);
var_dump($_SESSION["question"]->answers);
}
} else {
echo "<h2>no question selected.</h2>";
}
var_dump($_SESSION["question"]);
shows:
object(__PHP_Incomplete_Class)#2 (8) {
["__PHP_Incomplete_Class_Name"]=> string(8) "Question"
["id"]=> string(1) "1"
["correct"]=> NULL
["wrong"]=> NULL
["answers"]=> array(3) {
[0]=> object(__PHP_Incomplete_Class)#3 (5) {
["__PHP_Incomplete_Class_Name"]=> string(6) "Answer"
["correct"]=> string(1) "0"
["question_id":"Answer":private]=> NULL
["id"]=> string(1) "1"
["text"]=> string(9) "antwort 1"
}
[1]=> object(__PHP_Incomplete_Class)#4 (5) {
["__PHP_Incomplete_Class_Name"]=> string(6) "Answer"
["correct"]=> string(1) "0"
["question_id":"Answer":private]=> NULL
["id"]=> string(1) "2"
["text"]=> string(5) "ant 2"
}
[2]=> object(__PHP_Incomplete_Class)#5 (5) {
["__PHP_Incomplete_Class_Name"]=> string(6) "Answer"
["correct"]=> string(1) "0"
["question_id":"Answer":private]=> NULL
["id"]=> string(1) "3"
["text"]=> string(5) "ant 3"
}
}
["creator_id"]=> NULL
["categories"]=> array(0) { }
["text"]=> string(17) "eine Test frage ?"
}
but var_dump($_SESSION["question"]->answers); shows NULL.
I don't really understand that.
I got this as error message:
PHP Notice: main(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "Question" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition
Thanks for your help.

Answer 1

You need to run session_start() before you try to interact with the session object.
Also, you need to define your object before you call session_start(), or else the PHP's session handler won't know how to deserialise the object. That's why you see __PHP_Incomplete_Class.
EDIT: I found this answer that may help you PHP __PHP_Incomplete_Class Object with my $_SESSION data

Answer 2

I had to place session_start after my class definitions. Thanks to Progrock
include './entities/Answer.php';
include './entities/Question.php';
include './Database.php';
session_start();