Flask - UndefinedError: 'restaurant_id' is undefined

I try to reference another page from this page

<html>
    <head>
    </head>
    <body>
          <header>
              <h1>Restaurants<h1>
          </header>


          {% for i in restaurants %}

          <h5>
              <a href= "*">
                  {{i.name}}
              </a>
            &nbsp &nbsp
              <a href = "*">  Edit </a> &nbsp
              <a href = "*">  Delete  </a>
          </h5>

           {% endfor %}

        <a href = {{url_for('newRestaurant', restaurant_id = restaurant_id)}}> Create new restaurant </a>
    </body>
</html>

Here is my web server from where I manage the routes:

from flask import Flask, render_template, request, redirect, url_for, flash
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
from database_setup import Base, Restaurant, MenuItem

app = Flask(__name__)

engine = create_engine('sqlite:///restaurantmenu.db')
Base.metadata.bind = engine

DBSession = sessionmaker(bind = engine)
session = DBSession()

# Show all restaurants 
.....

#Create new restaurants
@app.route('/restaurant/<int:restaurant_id>/new', methods = ['GET','POS'])
def newRestaurant(restaurant_id):
    if request.method == 'POST':
        new_Restaurant = Restaurant(name = request.form['new_restaurant_name'], restaurant_id = restaurant_id)
        session.add(new_Restaurant)
        session.commit()
    #return "This page will be for making a new restaurant"
        flash("new restaurant create")
        return redirect(url_for('restaurants', restaurant_id = restaurant_id))
    else:
        return render('newRestaurant.html', restaurant_id = restaurant_id)

Here I am trying to route to my create restaurant page :

if __name__ == '__main__':
    app.debug = True
    app.run(host='0.0.0.0', port=5000)

Solution

You don't send anything to restaurant_id in the jinja template:

{{url_for('newRestaurant', restaurant_id = restaurant_id)}}

the second restaurant_id is not defined because you're not sending any value through it to the template.

You should send a number from your newRestaurant function.

For example (and this is only a simple example), you could verify if there is no row in the Restaurant table and if it isn't you initiate restaurant_id = 1:

EDITED

@app.route('/restaurant/<int:restaurant_id>', methods = ['GET','POST'])
def newRestaurant(restaurant_id):
    if request.method == 'POST':
        .............
    else:
        restaurants = session.query(Restaurant).all()
        if not restaurants:
            restaurant_id = 1
        else:
            nr_restaurants = session.query(Restaurant).count()
            restaurant_id = int(nr_restaurants) + 1
        return render_template('newRestaurant.html', restaurant_id = restaurant_id)

now you are sending a number to the template through restaurant_id variable and you can use it there.