protected static $member _id; What do you mean by this line of code? I didn't write it that way.

protected stationary $member _id;

class TokenController extends CommonController{    protected static $member_id;

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protected stationary $member _id;

class TokenController extends CommonController{    protected static $member_id;

Static is a class member, not an object member.
Protected is the only class and derived class that can access it.

When a static class allows a derived class to access a member, use this notation

    class A    {        public static $abc;            protected static $bbc;                public static function a()        {            return self.$bbc;        }    }可以直接 A.$abc来访问$abc这个变量A.a() 可以得到A.$bbc

Class member variable, the manipulation of this variable can only be controlled by the function, so that the query code which set get can be used.
Because only get set changes the value

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