Fix circular imports issue by separating SQLAlchemy db instance into database.py

.flaskenv

@@ -1 +1,2 @@
 FLASK_APP=app.py
+FLASK_ENV=development

app.py

@@ -9,8 +9,7 @@ from flask import Flask, render_template, request
 from flask_login import LoginManager, current_user
 from flask_sqlalchemy import SQLAlchemy
 from werkzeug.security import generate_password_hash
-
-db = SQLAlchemy()
+from database import db
 
 
 def create_app():
@@ -25,7 +24,7 @@ def create_app():
     # Heroku deployment
     if app.config['ENV'] == 'production':
         app.config['SECRET_KEY'] = os.getenv('SECRET_KEY')
-        app.config['SQLALCHEMY_DATABASE_URI'] = os.getenv('DATABASE_URL').replace('postgres://', 'postgresql://', 1)
+        app.config['SQLALCHEMY_DATABASE_URI'] = os.getenv('DATABASE_URL', '').replace('postgres://', 'postgresql://', 1)
 
     db.init_app(app)
 

auth.py

@@ -3,7 +3,7 @@ from flask_login import login_required, login_user, logout_user, current_user
 from werkzeug.security import check_password_hash, generate_password_hash
 
 from models import User
-from app import db
+from database import db
 
 blueprint = Blueprint('auth', __name__)
 

database.py

@@ -0,0 +1,3 @@
+from flask_sqlalchemy import SQLAlchemy
+
+db = SQLAlchemy()

forms.py

@@ -1,7 +1,7 @@
 from flask import Blueprint, flash, redirect, request, url_for
 from flask_login import current_user, login_required
 
-from app import db
+from database import db
 from models import User, Post, Comment
 
 blueprint = Blueprint('forms', __name__)

models.py

@@ -6,7 +6,7 @@ import humanize
 from flask_login import UserMixin
 from sqlalchemy import func
 
-from app import db
+from database import db
 
 MAXIMUM_ONLINE_DELTA = datetime.timedelta(minutes=1)