如何将超类实例转换为子类实例？ （教义）

I would like to use Class Table Inheritance:

/**
 * @Entity
 * @InheritanceType("JOINED")
 * @DiscriminatorColumn(name="discr", type="string")
 * @DiscriminatorMap({"player" = "Player", "admin" = "Admin"})
 */
class User
{
    // ...
}

/** @Entity */
class Player extends User
{
    // ...
}

/** @Entity */
class Admin extends User
{
    // ...
}

My question is:

If I have a Collection of Users, how is it possible to check, which one is an Admin and which one is a Player. And how to call a method of the subclass after that?

How do you manage to get a collection of Users?

Doctrine instantiates concrete classes of Player and Admin depending on value of DiscriminatorColumn. You can check which entity you get with instanceof:

switch(true){
    $entity instanceof Player:
         // do player's stuff
         break;
    $entity instanceof Admin:
         // do admin's stuff
         break;
}