Using proper file structure with SQLAlchemy and how to add data to db

Question

I am trying to build a simple blogging platform to learn Python and Flask. I am using SQLAlchemy to connect to a Postgres db hosted on Heroku and flask_s3 to serve static files from an AWS bucket. Im mostly following along from this:

https://gist.github.com/mayukh18/2223bc8fc152631205abd7cbf1efdd41/

All was going well, it is correctly hosted on Heroku and connceted to AWS S3 bucket, ready to go. I am stuck however on how to add blog posts to the database through some kind of form or route that will allow me to fill in the attributes of a blog post (found in Post in models.py below)

I have html templates that get rendered and the following three files, app.py, manage.py and models.py.

app.py:

from flask import Flask, render_template
from flask_sqlalchemy import SQLAlchemy
from flask_s3 import FlaskS3

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = '*URI for DB hosted on heroku'
app.config['FLASKS3_BUCKET_NAME'] = 'my S3 bucket on AWS'

db = SQLAlchemy(app)
s3 = FlaskS3(app)

from models import Post

#routes to templates to be rendered

if __name__ == '__main__'
    app.run(debug=True)

manage.py:

from flask_script import Manager
from flask_migrate import Migrate, MigrateCommand

from app import app, db

migrate = Migrate(app, db)

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

if __name__ == '__main__':
    manager.run()

and models.py:

from manage import db,app

class Post(db.Model):
    __tablename__ = 'blogposts'

    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(120), index=True, unique=True)
    content = db.Column(db.Text, index=True, unique=True)
    date = db.Column(db.DateTime, index=True, unique=True)
    tag = db.Column(db.String(120), index=True, unique=True)
    cover = db.Column(db.String(120), index=True, unique=True)

    def __repr__(self):
        return '<Post: %r>' % (self.title)

my file strucure is:

-blog
  --__pycache__
  --migrations
  --static
  --templates
  app.py
  manage.py
  models.py
  Pipfile
  Pipfile.lock
  Procfile

I want to work on this locally (before I publish anything to Heroku) but have no idea what to do from here. Anyone have advice on how to go about creating a route to add blog posts and saving them to a local Postgres instance before I go about pushing finalized blog posts to Heroku?

the gist I have been following has something like this as a route:

@app.route('/add/')
def webhook():
    #post attributes defined
    p = Post(id = id, title = title, date = datetime.datetime.utcnow, content = content, tag = tag, cover = cover)
    print("post created", p)
    db.session.add(p)
    db.session.commit()
    return "post created"

when I try and run it locally I get the following error so I'm not sure I have the files connecting properly.

File "/Users/Mb/Desktop/datadude/app.py", line 15, in <module>
from models import Post
ImportError: cannot import name 'Post'

Sorry if this is the wrong place for this. If there is a better place to ask for advice let me know.

Rafał · Accepted Answer · 2018-08-09 09:00:33Z

11

The problem exists in circular dependencies.

You could move initializing of SQLAlchemy to models.py. Then only run method init_app on db object in app.py.

models.py

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()

class Post(db.Model):
    __tablename__ = 'blogposts'

    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(120), index=True, unique=True)
    content = db.Column(db.Text, index=True, unique=True)
    date = db.Column(db.DateTime, index=True, unique=True)
    tag = db.Column(db.String(120), index=True, unique=True)
    cover = db.Column(db.String(120), index=True, unique=True)

    def __repr__(self):
         return '<Post: %r>' % (self.title)

app.py

import datetime
from flask import Flask, render_template

from flask_s3 import FlaskS3
from models import db


app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = '*URI for DB hosted on heroku'
app.config['FLASKS3_BUCKET_NAME'] = 'my S3 bucket on AWS'
db.init_app(app)

s3 = FlaskS3(app)
from models import Post


@app.route('/add/')
def webhook():
    #post attributes defined
    p = Post(id = id, title = title, date = datetime.datetime.utcnow, content = content, tag = tag, cover = cover)
    print("post created", p)
    db.session.add(p)
    db.session.commit()
    return "post created"
#routes to templates to be rendered

if __name__ == '__main__':
    app.run(debug=True)

You can read more about it https://github.com/slezica/bleg/blob/master/data/posts/2014-03-08-avoiding-circular-dependencies-in-flask.md

answered Aug 9, 2018 at 9:00

Rafał

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1 Comment

Felix Benning Over a year ago

any advice on where to put create_tables? I assume it has to be after init_app since that includes the database uri. So you would put it into app.py I guess?

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