What is the difference between session and db.session in SQLAlchemy?

Question

In case the display level is docs it says that Session.add() not supported, but when I tried to execute db.session.add(some_object) inside after_insert , it worked, for example:

 def after_insert_listener(mapper, connection, user): global_group = Group.query.filter_by(groupname='global').first() a = Association(user,global_group) db.session.add(a) event.listen(User, 'after_insert', after_insert_listener) 

Basically, any new user should be part of global_group, so I added it to the after_insert event. I tried to insert the user and then check in my database, and I found the user record and association record.

Answer 1

Let me check the differences:

 from flask import Flask from flask.ext.sqlalchemy import SQLAlchemy app = Flask(__name__) app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite://///Users/dedeco/Documents/tmp/testDb.db' db = SQLAlchemy(app) >>>type(db.session) <class 'sqlalchemy.orm.scoping.scoped_session'> 

or

 from sqlalchemy import * from sqlalchemy.orm import sessionmaker from sqlalchemy.ext.declarative import declarative_base some_engine = create_engine('sqlite://///Users/dedeco/Documents/tmp/testDb.db') Session = sessionmaker(bind=some_engine) session = Session() Base = declarative_base() >>> type(session) <class 'sqlalchemy.orm.session.Session'> 

Basically the difference:

• First of all, you use the API developed for the flash framework called Flask-SQLAlchemy. This is an option if you are creating a Flask application because the scope of the session can be controlled automatically by your application. You have many advantages, such as the infrastructure for creating a single session associated with the request, which is correctly constructed and torn down accordingly at the end of the request.

• In the second case, it is just an SQLAlchemy application, so if you use the library to connect a specific database, you can only use the SQLAlchemy API, for example, for the command line script, background daemon, GUI, etc.

So, in both directions you can add, for example:

Using Flask-SQLAlchemy :

 class User(db.Model): __tablename__ = 'users' user_id = db.Column(db.Integer(), primary_key = True) user_name = db.Column(db.String(80), unique=True) def __init__(self, user_name): self.user_name = user_name >>> db.create_all() >>> u = User('user1') >>> db.session.add(u) >>> db.session.commit() >>> users = db.session.query(User).all() >>> for u in users: ... print u.user_name ... user1 

Using only SQLAlchemy :

 class User(Base): __tablename__ = 'users' user_id = Column(Integer(), primary_key = True) user_name = Column(String(80), unique=True) >>> u = User() >>> u.user_name = 'user2' >>> session.add(u) >>> session.commit() >>> users = session.query(User).all() >>> for u in users: ... print u.user_name ... user1 user2 

Understand that I am connecting in the same database only to show what you can add in different ways.