Two concurrent sessions in Flask-SQLAlchemy

gistfile1.py

# coding=utf-8
import flask
from flask.ext.sqlalchemy import SQLAlchemy

app = flask.Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///:memory:'
app.config['SQLALCHEMY_ECHO'] = True

db = SQLAlchemy(app)
log_db = SQLAlchemy(app, session_options={
    'autocommit': True,
    'autoflush': False
})

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)

class Log(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    line = db.Column(db.Text)
    user_id = db.Column(db.Integer, db.ForeignKey(User.id))
    user = db.relationship(User)

    def __repr__(self):
        return '[%d] %s' % (self.user_id, self.line)

db.create_all()

with app.test_request_context():
    u = User()
    db.session.add(u)
    db.session.commit()

    u2 = User()
    db.session.add(u2)
    
    # 다음 줄은 u가 이미 db.session에 붙어있어서 오류
    #log_db.session.add(Log(line='hi', user=u))
    log_db.session.add(Log(line='hi', user_id=u.id))
    log_db.session.flush()
    #log_db.session.commit() # autocommit=True라서 안해도 됨

    print log_db.session.query(Log).all()
    db.session.commit()

Do you use this pattern to avoid transaction overhead on operations that dont require them?

flask sqlalchemy set autocommit = 0 default, and your operation to set autocommit = True is fail.You can use Neor profile sql to catch sql statement what you send.