Flask backref returing empty list - python-3.x

Question

I did ask this question but i am gonna ask it again since didn't get any response
I am developing a simple flask app with Projects and Tickets tables and they look like following
class Projects(db.Model):
id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.String(100), nullable = False)
description = db.Column(db.Text, nullable = False)
created_by_id = db.Column(db.Integer, nullable = False)
expert_id = db.Column(db.Integer, db.ForeignKey('users.id'))
def __repr__(self):
return f"{self.title}"
class Tickets(db.Model):
id = db.Column(db.Integer,primary_key=True)
title = db.Column(db.String(100),nullable=False)
ticket_text = db.Column(db.Text,nullable=False)
date_posted = db.Column(db.DateTime,nullable=False,default=datetime.utcnow)
created_by_id = db.Column(db.Integer, nullable=False)
expert_id = db.Column(db.Integer, db.ForeignKey('users.id'),nullable=False)
project_id = db.Column(db.Integer, db.ForeignKey('projects.id'),nullable=False)
projects = db.relationship('Projects', backref='ticketso', lazy=True)
def __repr__(self):
return f"Tickets('{self.title}','{self.date_posted}')"
Basically it is one Project can have many Tickets but when I query it
#app.route('/project/<project_id>')
def project(project_id):
project = Projects.query.get_or_404(project_id)
return render_template('project.html',title=project.title, project=project)
and trying to display it
<div class="jumbotron">
<h1>{{ project.title }}</h1>
<p>{{ project.description }}</p>
<p><a class="btn btn-primary btn-md">{{ project.created_by_id }}</a></p>
<p><a class="btn btn-primary btn-lg">{{ project.ticketso }}</a></p>
</div>
Here project.ticketso supposed to return list of tickets assigned to this Project but instead it returns emtpy list
My tickets.html page can succecfully display Project_id which assigned to that particular ticket
this is how I add ticket to the project
#app.route('/createTicket',methods=['GET','POST'])
def createTicket():
users = Users.query.all()
form = TicketForm()
if form.validate_on_submit():
ticket = Tickets(title=form.title.data,ticket_text=form.ticket_text.data,created_by_id=current_user.username,expert_id= str(form.user_id.data),project_id= str(form.project.data))
db.session.add(ticket)
db.session.commit()
flash('Your ticket has been created', 'success')
return redirect(url_for('index'))
return render_template('createTicket.html',title='Create a Ticket',form=form, users=users)
#app.route('/createProject',methods=['GET','POST'])
def createProject():
users = Users.query.all()
form = ProjectForm()
if form.validate_on_submit():
project = Projects(title = form.title.data, description = form.description.data, created_by_id = current_user.username, expert_id = str(form.user_id.data))
db.session.add(project)
db.session.commit()
flash('You project has been created', 'success')
return redirect(url_for('index'))
return render_template('createProject.html',form = form, users = users)
EDIT:
I am gonna ask this question different way in order to make it clear.
class Person(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(50), nullable=False)
addresses = db.relationship('Address', backref='person', lazy=True)
class Address(db.Model):
id = db.Column(db.Integer, primary_key=True)
email = db.Column(db.String(120), nullable=False)
person_id = db.Column(db.Integer, db.ForeignKey('person.id'),
nullable=False)
The code above I got from flask documentation https://flask-sqlalchemy.palletsprojects.com/en/2.x/models/
It states
backref is a simple way to also declare a new property on the Address class. You can then also use my_address.person to get to the person at that address
So I can access to the person who is in that address, but how do we access to the list of addresses that person has. Because it is one to many relationship, it means one person can have many addresses correct? how do we access them?

Answer 1

You need to "connect" between the 2 tables. You don't need to define expert_id when you create a row. instead you need to point to the Tickets Table by the backref you set.
Change this line
project = Projects(title = form.title.data, description = form.description.data, created_by_id = current_user.username, expert_id = str(form.user_id.data))
To this:
project = Projects(title = form.title.data, description = form.description.data, created_by_id = current_user.username, ticketso=form)
assuming form is the Tickets object you want to point to. Then, you'll be able to get the ID of the Tickets with expert_id
basically, this line projects = db.relationship('Projects', backref='ticketso', lazy=True) creates a "virtual column" in the table you set. In this case is the Projects table (You can also access the Projcts table from Tickets by using the relationship column). Also this two columns are useless. I assume you know how you can access the data without them.
expert_id = db.Column(db.Integer, db.ForeignKey('users.id'),nullable=False)
project_id = db.Column(db.Integer, db.ForeignKey('projects.id'),nullable=False)