Login_user not working without set session?

#! /usr/bin/env python

from models import *
from forms import *
from flask import Flask
from flask import g, url_for, render_template, redirect, flash, request, session
from flask_bcrypt import check_password_hash
from flask_login import LoginManager, login_user, logout_user, login_required


DEBUG = True
HOST = '0.0.0.0'
PORT = 8000


app = Flask(__name__)
app.secret_key = 'fgjdhf@897^*jdsf&^hdsjfh2si(*jddsk'
login_mgr = LoginManager()
login_mgr.init_app(app)
login_mgr.login_view = 'sign_in'

@login_mgr.user_loader
def load_user(userid):
    try:
        return User.get(User.id == userid)
    except models.DoseNotExist:
        return None


@app.before_request
def before_request():
    """ Before the request action """
    g.db = models.DATABASE
    try:
        g.db.connect()
    except OperationalError:
        pass


@app.after_request
def after_request(response):
    """ After the request """
    try:
        g.db.close()
        return response
    except Exception as e:
        pass


@app.route('/sign-in', methods=['GET', 'POST'])
def sign_in():
    form = SignInForm()
    if form.validate_on_submit():
        try:
            user = User.get(User.email == form.email.data)
        except User.DoesNotExist:
            flash("Email or password is incorrect", 'error')
        else:
            if check_password_hash(user.password, form.password.data):
                login_user(user)
                # Adding this line will make it works
                # session['user_id'] = user.id
                flash("You've been logged in!", "success")
                return redirect(url_for('index'))
            else:
                flash("Email or password is incorrect", 'error')
    return render_template('sign_in.html', form=form)


@app.route('/sign-up', methods=['GET', 'POST'])
def sign_up():
    form = RegisterForm()
    if form.validate_on_submit():
        User.new(username=form.username.data, password=form.password.data, email=form.email.data)
        return redirect(url_for('index'))
    return render_template('sign_up.html', form=form)

@app.route('/sign-out')
@login_required
def sign_out():
    logout_user()
    return redirect(url_for('index'))

@app.route('/')
@login_required
def index():
    return "Hello"

if __name__ == '__main__':
    import models
    models.initialize()
    try:
        models.User.new(**{
            'username': 'Robust',
            'email':    'robust@gmail.com',
            'password': '123456',
        })
    except Exception as e:
        pass
    app.run(debug=DEBUG, port=PORT, host=HOST)

from peewee import *
from flask_bcrypt import generate_password_hash
from flask_login import UserMixin
import datetime


DATABASE = SqliteDatabase("social.db")

class User(UserMixin, Model):
    username =  CharField(unique=True)
    email =     CharField(unique=True)
    password =  CharField(max_length=255)
    joined_at = DateTimeField(default=datetime.datetime.now)
    is_admin =  BooleanField(default=False)
    is_active = BooleanField(default=False)

    class Meta(object):
        database = DATABASE
        order_by = ('-joined_at',)

    @classmethod
    def new(cls, **data):
        _password = generate_password_hash(data['password'])
        return cls.create(username=data['username'], email=data['email'], password=_password)

    def get_posts(self):
        return Post.select().where(Post.user == self)

    def get_stream(self):
        return Post.select().where(Post.user == self)


class Post(Model):
    timestamp = DateTimeField(default=datetime.datetime.now)
    user = ForeignKeyField(rel_model=User, related_name='posts')

    class Meta(object):
        database = DATABASE
        order_by = ('-timestamp',)


def initialize():
    DATABASE.connect()
    DATABASE.create_tables([User], safe=True)
    DATABASE.close()