SQLAlchemy create all does not create tables

Question

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   lt User  r gt     self username  admin   User  admin    admin example com   guest   User  guest    guest example com   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

User · Answer

This is probably not the main reason why the create_all() method call doesn't work for people, but for me, the cobbled together instructions from various tutorials have it such that I was creating my db in a request context, meaning I have something like:

# lib/db.py
from flask import g, current_app
from flask_sqlalchemy import SQLAlchemy

def get_db():
  if 'db' not in g:
    g.db = SQLAlchemy(current_app)
  return g.db

I also have a separate cli command that also does the create_all:

# tasks/db.py
from lib.db import get_db

@current_app.cli.command('init-db')
def init_db():
  db = get_db()
  db.create_all()

I also am using a application factory.

When the cli command is run, a new app context is used, which means a new db is used. Furthermore, in this world, an import model in the init_db method does not do anything, because it may be that your model file was already loaded(and associated with a separate db).

The fix that I came around to was to make sure that the db was a single global reference:

# lib/db.py
from flask import g, current_app
from flask_sqlalchemy import SQLAlchemy

db = None
def get_db():
  global db
  if not db:
    db = SQLAlchemy(current_app)
  return db

I have not dug deep enough into flask, sqlalchemy, or flask-sqlalchemy to understand if this means that requests to the db from multiple threads are safe, but if you're reading this you're likely stuck in the baby stages of understanding these concepts too.

User · Answer

If someone is having issues with creating tables by using files dedicated to each model  be aware of running the  quot create all quot  function from a file different from the one where that function is declared  So  if the filesystem is like this  Root   --app py      lt -- file from which app will be run --models ----user py       lt -- file with  quot User quot  model ----order py     lt -- file with  quot Order quot  model ----database py  lt -- file with database and  quot create all quot  function declaration  Be careful about calling the  quot create all quot  function from app py  This concept is explained better by the answer to this thread posted by  SuperShoot

User · Answer

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   lt User  r gt     self username  db create all   db session commit    admin   User  admin    admin example com   guest   User  guest    guest example com   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    admin example com   guest   User  guest    guest example com   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

[python] SQLAlchemy create_all() does not create tables

Examples related to python

Examples related to postgresql

Examples related to sqlalchemy