如何在PHP类中使用与DB的连接？

Question

So I'm writing this website that requires me to make User class where i need to fetch some data from DB but when i try $this->conn = new PDO(....) it throws me fatal error as following

Fatal error: Uncaught exception 'PDOException' with message 'You cannot serialize or unserialize PDO instances' in [no active file]:0 Stack trace: #0 [internal function]: PDO->__sleep() #1 {main} thrown in [no active file] on line 0

Class User:

private $idu = -1;
private $display_name = "";
private $permissions = [];
private $conn = "";

/**
 * User constructor.
 */

function __construct($idu)
{
    $this->conn = new PDO("mysql:host=localhost;dbname=lai","lai","lai");
    $this->conn->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $this->idu = $idu;
    $this->setDisplayName($idu);
}

//GETS DISPLAY NAME FROM DB FOR CURRENT USER
private function setDisplayName($idu){
    //$sql = "SELECT `display_name` FROM `users` WHERE `idu`='".$idu."'";
    //$q = $this->conn->prepare($sql);
    //$q->execute();
    //$result = $q->fetch(PDO::FETCH_ASSOC);

    //return $result['display_name'];
}

//GETS PERMISSIONS FROM DB FOR CURRENT USER
private function setPermissions($idu){

}

//RETURNS ID OF CURRENT USER
public function getIDU(){
    return $this->idu;
}

//RETURNS DISPLAY NAME FOR CURRENT NAME
public function getDisplayName(){
    return $this->display_name;
}

//RETURNS PERMISSIONS FOR CURRENT USER
public function getPermissions(){
    return $this->permissions;
}

I don't need to store connection inside the class, but need to be able to use DB in my class, I've also tried declaring

$conn = new PDO(....);

outside of the class, globally and it also didn't work

Answer 1

You store that instance of user somewhere, like in the session?

PHP wants to serialize that class somewhere in your code, and all of it's field, even the $conn field. In order to store the whole user instance in the session, then you should either:

1. remove the reference to the db (which is considered a good idea) and move it to some repository or mapper class to retreive and manipulate user objects.

2. write a __wakeup method inside your User class which returns an array of the properties to be serialized:

   public function __wakeup() { return ["idu", "display_name", "permissions"]; // no $conn here! } This way it wont try to serialize the connection resource.