Flask CURD SqlAlchemy one to many relationship example :

Project Setup

• Making the project as :

  mkdir flask_sqlalchemy_one_to_many_relationship_example
  cd flask_sqlalchemy_one_to_many_relationship_example
  

• Install flask:

   pip install flask
  

• Integrating SqlAlchemy

  pip install sqlalchemy
  

• Create EmployeeManagementSystem.py for development

• create folder structure like this :

  

• create db.py

   from flask_sqlalchemy import SQLAlchemy
   db = SQLAlchemy()
  

• Declaring Models: [models/app_model.py]

  from db.db import db
     
  class Employee(db.Model):
     id = db.Column(db.Integer, primary_key=True)
     name = db.Column(db.String(255), nullable=False)
     email = db.Column(db.String(255), nullable=False)
     contact = db.Column(db.String(10), nullable=False)
     addresses = db.relationship('Address', backref=db.backref('employee', uselist=True),
                                 cascade='all, delete-orphan', lazy=True, uselist=True)
     # delete parent record in one to many relationship in flask cascade='all, delete-orphan'
  
  
  class Address(db.Model):
     id = db.Column(db.Integer, primary_key=True)
     addr = db.Column(db.String(255), nullable=False)
     employee_id = db.Column(db.Integer, db.ForeignKey('employee.id'), unique=True, nullable=False)
  
     def __init__(self, addr):
         self.addr = addr
  
  
  

• create settings.py for configuration

  # configuration
  class Config:
     DEBUG = True
     # db
     SQLALCHEMY_DATABASE_URI = 'mysql://root:root@localhost/djangoapp'
     SQLALCHEMY_TRACK_MODIFICATIONS = False
  

• Make a runserver configuration

  from flask import Flask, render_template, request, redirect, flash
  from sqlalchemy.exc import IntegrityError
  
  from db.db import db
  from models.app_model import Employee, Address
  
  app = Flask(__name__)
  app.secret_key = 'asrtarstaursdlarsn'
  app.config.from_object('settings.Config')
  
  # initialization
  db.init_app(app)
  
  
  @app.route("/", methods=['GET', 'POST'])
  @app.route("/<int:employee_id>", methods=['GET'])
  def employeeHome(employee_id=None):
     if request.method == 'POST':
         # person data
         pid = request.form.get('id')
         name = request.form.get('name')
         contact = request.form.get('contact')
         email = request.form.get('email')
         # license data
         address_list = []
  
         for addressValue in zip(request.form.getlist('address')):
             address_list.append(Address(addressValue[0]))
  
         print(address_list)
         if pid:  # if id present update records
             employee = Employee.query.filter_by(id=pid).first()
             employee.name = name
             employee.email = email
             employee.contact = contact
             employee.addresses = address_list
             db.session.commit()
             flash('Looks like you have changed your Details!', "success")
         else:
             # id not None save record
             try:
                 employee_entry = Employee(name=name, email=email, contact=contact)
                 employee_entry.addresses = address_list
                 db.session.add(employee_entry)
                 db.session.commit()
                 flash('Employee Successfully saved!', "success")
             except IntegrityError as e:
                 flash(e, 'Something went wrong please try again later', "danger")
     employee = None
     addresses = [None, None]
  
     if employee_id:  # load record form edit form data
         employee = Employee.query.filter_by(id=employee_id).first()
         addresses = Address.query.filter_by(employee_id=employee_id)
     employees = Employee.query.all()
     return render_template('index.html', employees=employees, employee=employee, addresses=addresses)
  
  
  @app.route("/delete/<int:employee_id>", methods=['GET'])
  def deleteEmployee(employee_id):
     try:
         employee = Employee.query.filter_by(id=employee_id).first()
         print(employee)
         if employee:
             db.session.delete(employee)
             db.session.commit()
             flash('Looks like you have changed your Details!', "success")
         else:
             flash('Could not find any Employee to delete', "danger")
     except IntegrityError as e:
         flash('Something went wrong please try again later', "danger")
     return redirect("/")
  
  
  # run always put in last statement or put after all @app.route
  if __name__ == '__main__':
     app.run(host='localhost')
  
  # manager.run()
  
  

• create html file inside templates folder

  • check project directory for index.html file

• In order to run app:

    python app.py
  

• run on your browser

  • Your should run at: http://127.0.0.1:5000/