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I'm trying to integrate PostgreSQL and SQLAlchemy but SQLAlchemy.create_all() is not creating any tables from my models.
My code:
from flask import Flask from flask.ext.sqlalchemy import SQLAlchemy app = Flask(__name__) app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql+psycopg2://login:pass@localhost/flask_app' db = SQLAlchemy(app) db.create_all() db.session.commit() class User(db.Model): id = db.Column(db.Integer, primary_key=True) username = db.Column(db.String(80), unique=True) email = db.Column(db.String(120), unique=True) def __init__(self, username, email): self.username = username self.email = email def __repr__(self): return '<User %r>' % self.username admin = User('admin', '[email protected]') guest = User('guest', '[email protected]') db.session.add(admin) db.session.add(guest) db.session.commit() users = User.query.all() print users But I get this error: sqlalchemy.exc.ProgrammingError: (ProgrammingError) relation "user" does not exist
How can I fix this?
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Creating and Inserting Data into Tables By passing the database which is not present, to the engine then sqlalchemy automatically creates a new database.
Creating and Dropping Database Tables create_all() creates foreign key constraints between tables usually inline with the table definition itself, and for this reason it also generates the tables in order of their dependency.
Step 1 - Install the Flask-SQLAlchemy extension. Step 2 - You need to import the SQLAlchemy class from this module. Step 3 - Now create a Flask application object and set the URI for the database to use. Step 4 - then use the application object as a parameter to create an object of class SQLAlchemy.
One of which is that Flask-SQLAlchemy has its own API. This adds complexity by having its different methods for ORM queries and models separate from the SQLAlchemy API. Another disadvantage is that Flask-SQLAlchemy makes using the database outside of a Flask context difficult.
You should put your model class before create_all() call, like this:
from flask import Flask from flask_sqlalchemy import SQLAlchemy app = Flask(__name__) app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql+psycopg2://login:pass@localhost/flask_app' db = SQLAlchemy(app) class User(db.Model): id = db.Column(db.Integer, primary_key=True) username = db.Column(db.String(80), unique=True) email = db.Column(db.String(120), unique=True) def __init__(self, username, email): self.username = username self.email = email def __repr__(self): return '<User %r>' % self.username db.create_all() db.session.commit() admin = User('admin', '[email protected]') guest = User('guest', '[email protected]') db.session.add(admin) db.session.add(guest) db.session.commit() users = User.query.all() print users If your models are declared in a separate module, import them before calling create_all().
Say, the User model is in a file called models.py,
from flask import Flask from flask_sqlalchemy import SQLAlchemy app = Flask(__name__) app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql+psycopg2://login:pass@localhost/flask_app' db = SQLAlchemy(app) # See important note below from models import User db.create_all() db.session.commit() admin = User('admin', '[email protected]') guest = User('guest', '[email protected]') db.session.add(admin) db.session.add(guest) db.session.commit() users = User.query.all() print users Important note: It is important that you import your models after initializing the db object since, in your models.py _you also need to import the db object from this module.
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