'How to wire up migrations in Flask with declarative base?

I'm using the declarative Base in flask_sqlalchemy. In my database.py file I have the following:

from sqlalchemy import create_engine
# from sqlalchemy.orm import scoped_session, sessionmaker
# from sqlalchemy.ext.declarative import declarative_base
# from flask_sqlalchemy import SQLAlchemy

# engine = create_engine("postgresql://postgres:@localhost/video_comparisons", convert_unicode=True)
# db_session = scoped_session(sessionmaker(autocommit=False,
#                                          autoflush=False,
#                                          bind=engine))
# Base = declarative_base()
# Base.query = db_session.query_property()

# Session = sessionmaker(bind = engine)

# db = SQLAlchemy()

# def init_db():
#     # import all modules here that might define models so that
#     # they will be registered properly on the metadata.  Otherwise
#     # you will have to import them first before calling init_db()
#     import yourapplication.models
#     Base.metadata.create_all(bind=engine)

Now, each of my models imports the Base object from database.py. This avoids circular imports.

Next, I'm trying to wire up the Flask migration module, which should work like this:

db = SQLAlchemy(app)
migrate = Migrate(app, db)
manager = Manager(app)
manager.add_command('db', MigrateCommand)

As you can see, I need to pass db into the Migrate constructor. But I don't have a db object, because I'm using the declarative Base, not creating it with db = SQLAlchemy(app).

What's the best way to do this? In the docs, I can't see how to connect the Migrate object to the database with this syntax.

Thanks, Louise

flaskflask-sqlalchemy


Solution 1:[1]

You have to import the db object from database.py :)

Solution 2:[2]

#timepass.py
from database import Base, metadata
from sqlalchemy import Table
class Timepass(Base):
    __table__ = Table('timepass', metadata, autoload=True)

#user.py
from project import db
class User(db.Model):
    __tablename__ = "users"

    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    username = db.Column(db.String(15), unique=True)
    email = db.Column(db.String(50), unique=True)
    password = db.Column(db.String(80))

Solution 3:[3]

import os
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

URI = os.environ.get('SQLALCHEMY_DB_URI')

engine = create_engine(URI, echo=True)
Session = sessionmaker(bind=engine)

Base = declarative_base()

def get_engine():
    return engine

metadata=Base.metadata

for use, in factory method.

from flask_migrate import Migrate
import src.ext.database as db

migrate = Migrate()

def init_app(app):
    migrate.init_app(app, db)

in app.py your import init_app(app) This method, 100% Working...

BR :D

Solution 4:[4]

The key point is that you might not need Migrate along with declarative. Please refer to this page.

from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session, sessionmaker
from sqlalchemy.ext.declarative import declarative_base

engine = create_engine('sqlite:////tmp/test.db')
db_session = scoped_session(sessionmaker(autocommit=False,
                                         autoflush=False,
                                         bind=engine))
Base = declarative_base()
Base.query = db_session.query_property()

def init_db():
    # import all modules here that might define models so that
    # they will be registered properly on the metadata.  Otherwise
    # you will have to import them first before calling init_db()
    import yourapplication.models
    Base.metadata.create_all(bind=engine)

The last two lines will help you to build tables if they do not exist. In my opinion, the Migrate library might be no more required.

Sources

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Source: Stack Overflow

Solution Source
Solution 1 Louise
Solution 2
Solution 3 Richard Guesso
Solution 4

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