React, Flask-restful and SQLAlchemy – getting data from the database


I download the data from the backend when selecting the option from the Navbar component of Bulma framework. I use the useEffect hook to get the data to be read during component rendering. Then, a query to the backend is created, and a token is passed as a parameter, set when the user logs in. The response is sent from the backend in the form of a Promise object, from which if the query is completed successfully, the cursor variable is set (change of state with setCursor). Cursor and setCursor function are passed to the component from the parent App.js component as parameters (props), i.e.

import LoginForm from '../Forms/LoginForm/LoginForm'
import { useEffect } from "react";

function Contracts({token, putToken, cursor, setCursor}) {

        () => {
            const token = sessionStorage.getItem('token')
            fetch('/api/contract/' + token)
            .then(res => res.json()).then(data => setCursor(data)).catch((err) => console.log(err))
        }, [token, cursor],
    if (!token) {
        return <LoginForm putToken={putToken} />

In order for the component to refresh the data after successfully logging in, in the additional parameter of the useEffect method in the array, I put the token variable, which is set in the LoginForm.js component.

In order for the component to refresh the data after changing the cursor content, e.g. by adding a new contract, I have placed the cursor variable as an additional parameter of the useEffect method.

Individual data lines are placed in the table, i.e.

    {cursor && Object.keys(cursor).map((keyName, keyIndex) => 
    <tr key={keyIndex}>

Backend with Flask-restful:

In the file, I add another resource class:

from api.resources.contracts import AllContracts

api.add_resource(AllContracts, '/api/contract/<token>', endpoint='all_contracts')

In, I define the resource class:

from datetime import datetime
from flask import request
from flask_restful import Resource
from .. import db
from ..common.models import User, Contract

class AllContracts(Resource):
    def get(self, token):
        token = token.strip('"')
        user = User.query.filter_by(token=token).first()
        contracts = Contract.query.filter_by(customer=user.username).order_by(
        cursor = {}
        for i, contract in enumerate(contracts):
            cursor[i] = contract.serialize()
        return cursor

In the file I define, among others, how the Contract class inheriting from the Model class from SQLAlchemy is to be serialized:

from .. import db
from datetime import datetime

class Contract(db.Model):
    '''Model of contract between a contractor and a customer'''

    id = db.Column(db.Integer, primary_key=True)
    status = db.Column(db.String(10), nullable=False, default='open')
    contract_number = db.Column(db.String(20), nullable=False)
    contractor = db.Column(db.String(20), db.ForeignKey('user.username'), nullable=False)
    customer = db.Column(db.String(20), db.ForeignKey('user.username'), nullable=False)
    date_of_order = db.Column(db.Date, nullable=False, default=datetime.utcnow)
    date_of_delivery = db.Column(db.Date, nullable=False)
    pallets_position = db.Column(db.Integer)
    pallets_planned = db.Column(db.Integer, nullable=False)
    pallets_actual = db.Column(db.Integer)    
    warehouse = db.Column(db.String(10), nullable=False)

    def serialize(self):
        return {'id':,
                'status': self.status,
                'contract_number': self.contract_number,
                'contractor': self.contractor,
                'customer': self.customer,
                'date_of_order': datetime.strftime(self.date_of_order, '%Y-%m-%d'),
                'date_of_delivery': datetime.strftime(self.date_of_delivery, '%Y-%m-%d'),
                'pallets_position': self.pallets_position,
                'pallets_planned': self.pallets_planned,
                'pallets_actual': self.pallets_actual,
                'warehouse': self.warehouse 

React and Bulma navbar

Problems solved:

  1. How to collapse a burger menu when selecting options from the menu (by default, selecting options from the burger menu leaves the menu expanded).
  2. How to collapse a pull-down menu when selecting an option. (by default, the drop-down menu does not close when an option is selected)

re. 1

The menu finally collapses when an option is selected.
<div id="navbarBasicExample" className={`navbar-menu ${burgerActive? "is-active": ""}`}>
                <div class="navbar-start">
                <Link to="/" class="navbar-item" onClick={handleOnClick}>


    const [burgerActive, setBurgerActive] = useState(false)

    const handleOnClick = () => {

re. 2

The pull-down menu collapses when an option is selected.
<div class="navbar-item has-dropdown is-hoverable" key={location.pathname}>


import {
    Link, useLocation
  } from 'react-router-dom' 

const Navbar = () => {
    let location = useLocation();

Bulma navbar and React

Navbar as a React.js component.

Added support for the hamburger button.

Navbar.js file:

import React, { useState } from 'react'
import {
  } from 'react-router-dom' 

const Navbar = () => {
    const [burgerActive, setBurgerActive] = useState(false)
    return (
        <nav class="navbar" role="navigation" aria-label="main navigation">
            <div class="navbar-brand">
                <a class="navbar-item" href="">
                <div class="title">Contracts</div>

                <a role="button" className={`navbar-burger ${burgerActive? "is-active": ""}`} 
                    aria-label="menu" aria-expanded="false" 
                    onClick={() => setBurgerActive(!burgerActive)}
                <span aria-hidden="true"></span>
                <span aria-hidden="true"></span>
                <span aria-hidden="true"></span>

            <div id="navbarBasicExample" className={`navbar-menu ${burgerActive? "is-active": ""}`}>
                <div class="navbar-start">
                <Link to="/" class="navbar-item">

                <a class="navbar-item">

                <div class="navbar-item has-dropdown is-hoverable">
                    <a class="navbar-link">

                    <div class="navbar-dropdown">
                    <Link to="/about" class="navbar-item">
                    <a class="navbar-item">
                    <a class="navbar-item">
                    <hr class="navbar-divider"/>
                    <a class="navbar-item">
                        Report an issue

                <div class="navbar-end">
                <div class="navbar-item">
                    <div class="buttons">
                    <Link to="/user/register" class="button is-link">
                        <strong>Sign up</strong>
                    <Link to="/user/login" class="button is-light">
                        Sign In

export default Navbar

React & Flask # 1 – user registration


import React, {useState} from 'react'
import { useHistory } from "react-router-dom";
import {useForm} from "react-hook-form";
import './RegisterForm.css'
function RegisterForm() {

    let history = useHistory();

    const {register, handleSubmit, getValues, formState: { errors } } = useForm();

    const [userRole, setUserRole] = useState('')

    const onSubmit = (data, e) => {
        data['role'] = userRole
        fetch('/api/user/register', {
            method: 'POST',
            headers: {
                'Content-type': 'application/json',
            body: JSON.stringify(data)
        .then(res => console.log(res.json()))
    return (
        <div className="columns">
            <div className="column is-narrow-desktop is-offset-5">
                <div className="card is-3 mt-5">
                    <header className="card-header">
                        <p className="card-header-title has-text-primary-light has-background-dark">
                            User Registration
                    <div className="card-content">
                        <div className="content">
                            <form onSubmit={handleSubmit(onSubmit)}>
                                <div className="field">
                                    <div className="control">
                                        <select name="role" required
                                            onChange={(e) => setUserRole(}>
                                            <option value="" disabled defaultValue="" hidden>Role</option>
                                            <option value="Contractor" >Contractor</option>
                                            <option value="Customer">Customer</option>
                                <div className="field control">
                                    <input placeholder="Username" name="username" 
                                        {...register("username", {required: true, minLength: 3})} />
                                    <p className="help is-danger">
                                        {errors.username?.type === 'required' && "This field is required"}
                                        {errors.username?.type === 'minLength' && "This field must contain at least 3 characters"}
                                <div className="field control">
                                    <input placeholder="Email" id="email"
                                        {...register("email", {required: true, pattern: /\S+@\S+\.\S+/})} />
                                    <p className="help is-danger">
                                        { === 'required' && "This field is required"}
                                        { === 'pattern' && "Invalid email address"}
                                <div className="field control">
                                    <input type="password" placeholder="Password" id="password" name="password"
                                        {...register("password",  {required: true, minLength: 6})} />
                                    <p className="help is-danger">
                                        {errors.password?.type === 'required' && "This field is required"}
                                        {errors.password?.type === 'minLength' && "This field must contain at least 6 characters"}
                                <div className="field control">
                                    <input type="password" placeholder="Retype Password" id="confirm_password"
                                        {...register("confirm_password",  {required: true, minLength: 6,
                                            validate: value => value === getValues('password')})} />
                                    <p className="help is-danger">
                                        {errors.confirm_password?.type === 'required' && "This field is required"}
                                        {errors.confirm_password?.type === 'minLength' && "This field must contain at least 6 characters"}
                                        {errors.confirm_password?.type === 'validate' && "Passwords don't match"}

                                <div className="control">
                                    <input type="submit" value="Register" className="button is-link" />    


export default RegisterForm

Backend – main file: __init__py

def create_app(Config):
    app =  Flask(__name__, static_folder='../build', static_url_path='/')
    app.db = db
    bcrypt = Bcrypt(app)
    app.bcrypt = bcrypt

    from .common import utils
    from .common import routes
    return app

from api.resources.auth import UserRegister
api.add_resource(UserRegister, '/api/user/register', endpoint='user_register')

File that contains the Resource class for handling user registration:

from flask import current_app, request
from flask_restful import Resource
from api.common.parsers import parser
from ..common.utils import send_email
from ..common.models import User
from .. import db
class UserRegister(Resource):

    def post(self):
        req = request.json
        username = req['username']
        password = req['password']
        email = req['email']
        role = req['role']
        bcrypt = current_app.bcrypt
        hashed_password = bcrypt.generate_password_hash(password).decode('utf-8')
        status = send_email(email, category='confirm_account')
        user = User(username=username, password=hashed_password, email=email, role=role)
        return {"message": status}

Forms in React using React Hook Form

My sample login form:

import React from 'react'
import {useForm} from "react-hook-form"

function LoginForm() {

    const {register, handleSubmit,  formState: { errors } } = useForm();

    const onSubmit = (data, e) =>  {

    return (
        <form onSubmit={handleSubmit(onSubmit)}>

            <input placeholder="Enter username" id="username" 
                {...register("username", {required: true, minLength: 3})} />
            {errors.username?.type === 'required' && "This field is required"}
            {errors.username?.type === 'minLength' && "This field must contain at least 3 characters."}
            {/* {errors.username && <span>This field is required and must contain at least 3 characters.</span>} */}
            <input type="password" placeholder="Password" id="password" 
                {...register("password",  {required: true, minLength: 6})} />
            {errors.password?.type === 'required' && "This field is required"}
            {errors.password?.type === 'minLength' && "This field must contain at least 6 characters."}

            <input type="submit" value="Login" />    


export default LoginForm


React app router snippet

Main app component sample snippet with BrowserRouter:

import './App.css';
import {
} from 'react-router-dom' 
import LoginForm from './components/LoginForm/LoginForm'

function App() {
  return (
      <div className="App">
          <Route path="/" exact>
            <LoginForm />
            <Link to="/about">About</Link>
          <Route path="/about">
            <Link to="/">Go to main page</Link>
          <Route path="/to-component" component={LoginForm} />

export default App;

Order processing for Logistics Centers

The application allows the customer to place new orders and accept orders by the contractor as well as generate reservations, i.e. manage delivery time slots to central warehouses and logistics centers.

The source code for the application is available here.

You can try the app here.

In this post, I will introduce the new_booking(id) function which handles the booking for a specific order (contract). It takes the contract identification number as a parameter, i.e.

@bp.route('/booking/<int:id>', methods=['GET', 'POST'])
def new_booking(id):

Then, in the new_booking () function, I create a booking form and get the booking object for a given contract, i.e.

    form = BookingForm()
    result = Booking.query.filter_by(contract_id=id).first()

Next, I set the contract object for the booking, i.e.

    current_contract = Contract.query.get(id)     # Returns contract for current booking

In the following lines I get a list of orders that were generated for a specific warehouse on the day of delivery, i.e.

# Filtering by one column gives a list of tuple(s) so I converted it to a list of values
    contracts = [ids[0] for ids in Contract.query.with_entities(

Then I validate if the form has been submitted. Depending on whether the reservation for a given contract has already been created, I update the data in the database based on the data from the form. If the booking object does not exist, I create a new booking object and save it to the database, i.e.

    if form.validate_on_submit():
        if result:
            result.booking_time =
            result.driver_full_name =
            result.driver_phone_number =
            result.truck_reg_number =
            booking = Booking(, 
                            contract_id = id,

Next, I change the order status to accepted and redirect to the function displaying all orders for a given contractor, i.e.

        contract = Contract.query.get(id)
        contract.status = 'accepted'
        page = session.get('page')
        per_page = session.get('per_page')
        return redirect(url_for('contracts.contracts', page=page, per_page=per_page))

If the page is loaded using the GET method, then depending on whether the booking is already present in the system or is being created, the data is completed in the form, i.e. if the booking is available and we open it, e.g. to edit the data, then the form will be completed with the previous one entered data. However, if the reservation is just being created, the form will contain a modification, the dates of which cannot be selected, because they have already been selected by other suppliers, i.e.

    if result is not None:
        reserved_booking_time = [times[0] for times in 
            Booking.contract_id.in_(contracts)).all() if times[0]!=result.booking_time]   = result.booking_time = result.driver_full_name = result.driver_phone_number = result.truck_reg_number   
        reserved_booking_time = [times[0] for times in 
    return render_template('booking.html', form=form, reserved_booking_time=reserved_booking_time)

The complete code for the new_booking() function is available here.

A contract accepted in this way can only be edited by the customer. However, if the contract has already been accepted and the booking has been made, the change of the contract changes the status of the order from accepted back to open and requires the contractor to accept the changes again (but the entered data are present and the reservation is does not require data to be repeated).

The contractor may also download a pdf of the booking if the contract is accepted (for open contract the option to download pdf is inactive).

Reservation made – now you can generate pdf

Reportlab – generating and downloading pdf in Flask without creating the file on the server

Solved problem: how to generate pdf with order data and reservation barcode without saving the file on disk, which can then be downloaded by the website user in Flask.

We can use the Canvas object to embed document elements such as texts, tables, etc. As an argument we can give the name of the created pdf, but in this case I will use the buffer instead of creating the file on the server. I’m explicitly entering the page size as A4.

from io import BytesIO
from reportlab.pdfgen.canvas import Canvas
from reportlab.lib.pagesizes import A4

buffer = BytesIO()
canvas = Canvas(buffer, pagesize=A4)

To use non-standard characters, register the appropriate fonts that support the required characters. In the sample pdf file, I used the Vera font.

from reportlab.pdfbase import pdfmetrics
from reportlab.pdfbase.ttfonts import TTFont

pdfmetrics.registerFont(TTFont('Vera', 'Vera.ttf'))

The registered font can now be used:

canvas.setFont("Vera", size=10)

I place the images (in this case, the reservation barcode) generated on the basis of the data from the application in the document being created using the drawImage () method, which takes the ImageReader object as the first argument, i.e.

im = ImageReader(image)
canvas.drawImage(im, x=0, y=-5*cm, width=150, height=100)

A list of text strings can be added to a document using a text object, i.e.

txt_obj = canvas.beginText(14, -6.5 * cm)
txt_lst = ["line of text 1", "line of text 2", "line of text 3"]
for line in txt_lst:
        txt_obj.moveCursor(0, 16)

A table can be added to a document as a Table class object. I separately define a list containing the data of individual table rows (table_data variable). I also define styles that are valid for all or part of the table.

t = Table(table_data, colWidths=[60, 230, 70, 60, 50], rowHeights=30)
style = [('BACKGROUND',(0,0),(-1,-2),colors.lightblue),
            ('BOX', (0,0), (-1,-1), 0.25,,
            ('INNERGRID', (0,0), (-1,-1), 0.25,,
            ('FONTSIZE', (0,0), (-1,-1), 10),
            ('ALIGN', (0, 0), (-1, -1), 'CENTER'),
            ('VALIGN', (0, 0), (-1, -1), 'MIDDLE')]
t.wrapOn(canvas, 10, 10)
    t.drawOn(canvas=canvas, x=20, y=-22*cm)

Then I save the created Canvas object and return the resulting buffer to the controller. In order to send a pdf file based on data from the buffer, I use the send_file () Flask function:

from flask.helpers import send_file

@bp.route('/get-pdf/<int:id>', methods=['GET'])
def get_pdf(id):
    contract = Contract.query.get(id)
    contractor = User.query.get(contract.contractor_id)
    booking = Booking.query.filter_by(
    pdf = create_pdf(,
    return send_file(pdf, as_attachment=True, mimetype='application/pdf',
        attachment_filename='booking.pdf', cache_timeout=0)
sample file generated on the server side, downloaded by the contractor.

Time slot management system using Flask #2

The source code of the application can be downloaded here.

You can try the app here.

The plan for the application described in the previous article looks like this:

│ ├───api
│ ├───auth
│ │ ├───static
│ │ │ └───logos
│ │ ├───templates
│ │ │ └───auth
│ │ ├───utils
│ │ │ ├───templates
│ │ │ │ └───utils
│ ├───contracts
│ │ ├───static
│ │ ├───templates
│ │ │ └───contracts
│ │ │ └───errors
│ │ ├───utils
│ ├───static
│ ├───templates
│ ├───functional
│ ├───unit

Each part of the application is a separate entity. A similar solution is used in Django. I wrote the file to manage the application. Each component has its own template subdirectories – a convention similar to Django’s.