ตัวโหลดผู้ใช้และ UserMixin

The Flask-Login extension manages who is logged in for you. It tracks the current user across requests so you do not wire sessions by hand.

Everything starts with a LoginManager. You create one instance and connect it to your app so Flask-Login can hook into requests.

To work, the manager needs a user model that follows its rules and a function that loads a user by id. Today you set up both.

Your model must expose a few properties like is_authenticated. The UserMixin class supplies them all, so you just inherit from it.

UserMixin adds is_authenticated, is_active, is_anonymous, and get_id for free. That last one returns your user id as a string.

Flask-Login stores only the user id in the session. It calls your user_loader on each request to turn that id back into a real user.

Decorate a function with login_manager.user_loader. It receives the id from the session and must return a user object or None.

The id passed to your loader is always a string, since it came from a cookie. Cast it to int before querying an integer primary key.

If the id matches no row, your loader should return None. Flask-Login then treats the request as coming from an anonymous visitor.

If your primary key is not named id, override get_id so it returns the right value. Most apps with a plain id column never touch it.

With the manager, the UserMixin model, and a user_loader in place, Flask-Login can identify the current user on every incoming request.

Think about what the session actually stores between requests.

You wired a LoginManager, mixed UserMixin into your model, and wrote a user_loader. Flask-Login can now rebuild the current user from a session. 👤