Python Flask web application sample with SQL Server database

This topic explains all the steps needed to set up a python flask web application using SQL Server database.
Learn how to set up flask for first time in your machine, how to run the flask applications, basic set up for your first HTML page, database actions like create a record, fetch data, update a record and delete from your flask application.
In this sample, pyodbc adapter is used to connect to the SQL Server database.
Contents
Install Python and setup Virtual Environment

Install pyodbc

pyodbc Installation Error

Install Flask

Initial steps for Flask Web Apps
Setting up First page

SQL Server Database Setup

Fetch data from SQL Server DB and list

Insert new item to SQL Server DB
Update items - SQL Server DB

Delete an Item from SQL Server DB

Flask CRUD with SQL Server - Complete code

Other web app samples
Install Python and setup Virtual Environment

Download and install the latest version of python from Python Website.

Setting up virtual environment is not a must, but its is good to keep all your projects within a virtual environment. Here, we will proceed with a virtual environment.

For that, go to the command prompt and cd to the folder where you are going to keep your project.
Run command python -m venv CarSales to create a project folder CarSales and a virtual environment for it.
Activate the VE using command:

For Windows:

CarSales\Scripts\activate.bat

For Linux, macOS:

source CarSales /bin/activate

After VE activation, from cmd type cd CarSales to navigate to the project folder.
Install pyodbc

For SQL Server connection we are going to use the pyodbc library. For quick reference on pyodbc use this link pyodbc basics.
Install it using the command: pip install pyodbc

pyodbc installation may some times throw an error message like Microsoft Visual C++ 14.0 or greater is required.
Refer next section to fix this error.
pyodbc Installation Error - Microsoft Visual C++ 14.0 or greater is required

This issue is caused by the fact that the latest version of pyodbc is not optimised for the python version that is installed in our machines.
For example, at the time of writing this article, we had python 3.10.0 as the latest version in our machine and pyodbc version was 4.0.32 and this pyodbc version was throwing this error.
Follow the below steps to fix the issue.

Delete the already created virtual environment. Set it up again using the command.

For Windows:

py -3.9 -m venv <ProjectName>

For Linux, macOS:

python3.9 -m venv <ProjectName>

Then install pyodbc using command: pip3.9 install pyodbc
Install Flask

To install flask, run command pip install flask or pip3.9 install flask
If not working use commands:

For Windows:

py -3.9 -m pip install flask

For Linux, macOS:

python3.9 -m pip install flask

Run pip freeze or pip3.9 freeze to check if flask installed successfully. Should give an output like this.
```
    click==8.0.3
    colorama==0.4.4
    Flask==2.0.2
    itsdangerous==2.0.1
    Jinja2==3.0.3
    MarkupSafe==2.0.1
    pyodbc==4.0.32
    Werkzeug==2.0.2
```
Initial steps for Flask Web Apps

Follow these basic steps to set up your first Flask web application.
Create a file named carsales.py (you can provide any name) inside CarSales folder and copy below code to it. carsales.py is going to contain your start-up code which is required to run your webapp. Copy below code to the file. From command prompt navigate to CarSales folder and execute command py carsales.py or python carsales.py or py -3.9 -m carsales or python3.9 -m carsales (Depending on the Operating System and Python version used).
```
from flask import Flask

carsales = Flask(__name__)

if(__name__ == "__main__"):
    carsales.run()
```
This code imports Flask module and creates an object carsales of Flask class. Last 2 lines serves as the entry point of the app and starts the server. In cmd, we will see the below message.
```
    * Serving Flask app 'carsales' (lazy loading)
    * Environment: production
    WARNING: This is a development server.
	Do not use it in a production deployment.
    Use a production WSGI server instead.
    * Debug mode: off
    * Running on http://127.0.0.1:5000/ 
	Press CTRL+C to quit)
```
Copy the url http://127.0.0.1:5000/ to your browser and run. We will get the Not Found message as below.

This means that the Flask has handled the server set up and our application is ready. We will now have to set up our html pages and routing to handle page navigations.
Setting up First page

We are going to keep a list page as the first page of the application.
In Flask, all our HTML should be placed inside a folder named templates and static files like javascript or stylesheet should be placed inside static folder.So, create a folder structure as below within your application folder and add html file carslist.html inside templates folder.

Add below code to carslist.html. To handle routing for this page, modify carsales.py as below. This code imports render_template module and sets up the default route.
Copied

from flask import Flask, render_template carsales = Flask(__name__) @carsales.route("/") #For default route def main(): return render_template("carslist.html") if(__name__ == "__main__"): carsales.run()
Copied

<!DOCTYPE html> <html lang="en-US" dir="ltr"> <head> <title>Cars List</title> </head> <body> <h2>Cars List</h2> </body>
In command prompt. click Ctrl + C to stop the application and run command py -3.9 -m carsales or python3.9 -m carsales or py carsales or python carsales (Varies depending on os and the python version used). This process is to be done each time we make any changes and want to reload the page. Some times, after stopping flask web from command prompt, just reloading the html will not give you the desired output. If any such issues are faced, close the web page and reopen.

Database Setup

Connect to your SQL server instance and create a database CarSales. Set up login for the database (Not covered here). Create a table TblCars with below structure and insert below set of data.

CREATE TABLE [dbo].[TblCars](
	[ID] [int] NOT NULL,
	[Name] [varchar](100) NULL,
	[Year] [int] NOT NULL,
	[Price] [float] NOT NULL)

INSERT INTO TblCars VALUES (1, 'Toyota Camry', 2018, 2000)
INSERT INTO TblCars VALUES (2, 'Honda Civic', 2019, 2200)
INSERT INTO TblCars VALUES (3, 'Chevrolet Silverado', 2017, 1800)
INSERT INTO TblCars VALUES (4, 'Ford F-150', 2020, 2500)
INSERT INTO TblCars VALUES (5, 'Nissan Altima', 2021, 3000)

Fetch data from SQL Server DB and list

carslist.html is going to hold the list of cars available for sale. To list the items, add below code in body of html and modify carsales.py main method as below. Also import pyodbc. In python file, we are reading data from SQL Server database CarSales using pyodbc built-in functions as shown below and pass it to html as a parameter. In html, we are looping through the items and list it as table rows.

from flask import Flask, render_template
import pyodbc

carsales = Flask(__name__)

def connection():
    s = '' #Your server name 
    d = 'CarSales' 
    u = '' #Your login
    p = '' #Your login password
    cstr = 'DRIVER={ODBC Driver 17 for SQL Server};SERVER='+s+';DATABASE='+d+';UID='+u+';PWD='+ p
    conn = pyodbc.connect(cstr)
    return conn

@carsales.route("/")
def main():
    cars = []
    conn = connection()
    cursor = conn.cursor()
    cursor.execute("SELECT * FROM dbo.TblCars")
    for row in cursor.fetchall():
        cars.append({"id": row[0], "name": row[1], "year": row[2], "price": row[3]})
    conn.close()
    return render_template("carslist.html", cars = cars)

if(__name__ == "__main__"):
    carsales.run()

<table class="table">
    <thead>
        <tr>
        <th scope="col">Id</th>
        <th scope="col">Name</th>
        <th scope="col">Year</th>
        <th scope="col">Price</th>
        </tr>
    </thead>
    <tbody>
        {% for car in cars %}
            <tr>
                <td>{{ car.id }}</th>
                <td>{{ car.name }}</td>
                <td>{{ car.year }}</td>
                <td>{{ car.price }}</td>
            </tr>
        {% endfor %}
    </tbody>
</table>

For styling we will use Bootstrap 5. Add below 2 lines inside head of html.


    <link rel="stylesheet" crossorigin="anonymous"
	href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" >
    
	<script crossorigin="anonymous"
	src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/js/bootstrap.bundle.min.js" >
	</script>

On rerun, we will get below output window.

Insert new item to SQL Server DB

Add a new button in the carslist.html above the table.

    <a class="btn btn-primary" href="addcar">Add New Car</a>

Add new html file, addcar.html and place below code. Add below code in caresales.py as the second route below main method.

@carsales.route("/addcar", methods = ['GET','POST'])
def addcar():
    if request.method == 'GET':
        return render_template("addcar.html")
    if request.method == 'POST':
        id = int(request.form["id"])
        name = request.form["name"]
        year = int(request.form["year"])
        price = float(request.form["price"])
        conn = connection()
        cursor = conn.cursor()
        cursor.execute("INSERT INTO dbo.TblCars (id, name, year, price) VALUES (?, ?, ?, ?)", id, name, year, price)
        conn.commit()
        conn.close()
        return redirect('/')

<!DOCTYPE html>
<html lang="en-US" dir="ltr">
<head>
    <title>Car Details</title>
    
    <link rel="stylesheet" crossorigin="anonymous"
	href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" >
    
	<script crossorigin="anonymous"
	src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/js/bootstrap.bundle.min.js" >
	</script>

</head>

<body>
    <h2>Car Details</h2>

    <form action="" method = "POST">
        <div class="form-group row">
          <label for="id">Id</label>
          <input type="text" class="form-control" name="id" id="id">
        </div>
        <div class="form-group row">
            <label for="name">Maker and Model</label>
            <input type="text" class="form-control" name="name" id="name">
        </div>
        <div class="form-group row">
            <label for="year">Make Year</label>
            <input type="text" class="form-control" name="year" id="year">
        </div>
        <div class="form-group row">
            <label for="price">Sell Price</label>
            <input type="text" class="form-control" name="price" id="price">
        </div>
        <button type="btnAdd" class="btn btn-primary">Submit</button>
        <a href="/" class="btn btn-primary">Cancel</a>
      </form>
</body>

Now we have to import request and redirect. For that, change first line as below.

from flask import Flask, render_template, request, redirect

In the python code, we are defining a new route for addcar. We are using the same method for GET and POST. GET is just rendering addcar.html. In POST, we are reading data from form controls and save data to table and then redirect to list page.

In HTML page, we are defining a form with 4 text boxes. Each has a name provided. This name is used in the python file while reading data from controls.
On rerun, we can navigate to Create page as below and add new Car.

Update items - SQL Server DB

For update and delete we will add 2 links in the carslist.html page as below.

<table class="table">
    <thead>
        <tr>
        <th scope="col">Id</th>
        <th scope="col">Name</th>
        <th scope="col">Year</th>
        <th scope="col">Price</th>
        <th scope="col">Edit</th>
        <th scope="col">Delete</th>
        </tr>
    </thead>
    <tbody>
        {% for car in cars %}
            <tr>
                <td>{{ car.id }}</th>
                <td>{{ car.name }}</td>
                <td>{{ car.year }}</td>
                <td>{{ car.price }}</td>
                <td><a href='updatecar/{{ car.id }}'>Edit</a></td>
                <td><a href='deletecar/{{ car.id }}'>Delete</a></td>
            </tr>
        {% endfor %}
    </tbody>
</table>

For easier understanding, we are going to keep separate routes for create and update, although we are using the same addcar.html for update also. For update we will provide the route name updatecar.
In addcar.html, in order to populate the values, we have to use the value attribute and bind the car object values as in html provided below.

In carsales.py, add new updatecar route. In GET, we are filtering details based on selected id and using fetchall() function, assigning it to a list variable and pass it to the addcar.html page.
In POST, we are using the update command and commit
Note: We have to disable Id textbox to not make changes to Id. Here we are not doing it and if Id is changed no update will happen.

@carsales.route('/updatecar/<int:id>',methods = ['GET','POST'])
def updatecar(id):
    cr = []
    conn = connection()
    cursor = conn.cursor()
    if request.method == 'GET':
        cursor.execute("SELECT * FROM dbo.TblCars WHERE id = ?", id)
        for row in cursor.fetchall():
            cr.append({"id": row[0], "name": row[1], "year": row[2], "price": row[3]})
        conn.close()
        return render_template("addcar.html", car = cr[0])
    if request.method == 'POST':
        name = str(request.form["name"])
        year = int(request.form["year"])
        price = float(request.form["price"])
        cursor.execute("UPDATE dbo.TblCars SET name = ?, year = ?, price = ? WHERE id = ?", name, year, price, id)
        conn.commit()
        conn.close()
        return redirect('/')

<!DOCTYPE html>
<html lang="en-US" dir="ltr">
<head>
    <title>Car Details</title>
    
    <link rel="stylesheet" crossorigin="anonymous"
	href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" >
    
	<script crossorigin="anonymous"
	src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/js/bootstrap.bundle.min.js" >
	</script>

</head>

<body>
    <h2>Car Details</h2>

    <form action="" method = "POST">
        <div class="form-group row">
          <label for="id">Id</label>
          <input type="text" class="form-control" name="id" id="id" value="{{car.id}}">
        </div>
        <div class="form-group row">
            <label for="name">Maker and Model</label>
            <input type="text" class="form-control" name="name" id="name" value="{{car.name}}">
        </div>
        <div class="form-group row">
            <label for="year">Make Year</label>
            <input type="text" class="form-control" name="year" id="year" value="{{car.year}}">
        </div>
        <div class="form-group row">
            <label for="price">Sell Price</label>
            <input type="text" class="form-control" name="price" id="price" value="{{car.price}}">
        </div>
        <button type="btnAdd" class="btn btn-primary">Submit</button>
        <a href="/" class="btn btn-primary">Cancel</a>
      </form>
</body>

After the above changes, update will work, but create will throw an error. To fix this, change the render_template line of addcar as below.

return render_template("addcar.html", car = {})

We are binding an empty car object to make it working.

Delete an Item from SQL Server DB

For delete, we will add a new route deletecar. And just need to provide delete query as below. If needed, a confirm popup also can be added.
Copied
```
@carsales.route('/deletecar/<int:id>')
def deletecar(id):
    conn = connection()
    cursor = conn.cursor()
    cursor.execute("DELETE FROM dbo.TblCars WHERE id = ?", id)
    conn.commit()
    conn.close()
    return redirect('/')
```

Flask CRUD with SQL Server database - Complete code

Complete code is placed below.

from flask import Flask, render_template, request, redirect
import pyodbc

carsales = Flask(__name__)

def connection():
    s = '' #Your server name 
    d = 'CarSales' 
    u = '' #Your login
    p = '' #Your login password
    cstr = 'DRIVER={ODBC Driver 17 for SQL Server};SERVER='+s+';DATABASE='+d+';UID='+u+';PWD='+ p
    conn = pyodbc.connect(cstr)
    return conn

@carsales.route("/")
def main():
    cars = []
    conn = connection()
    cursor = conn.cursor()
    cursor.execute("SELECT * FROM dbo.TblCars")
    for row in cursor.fetchall():
        cars.append({"id": row[0], "name": row[1], "year": row[2], "price": row[3]})
    conn.close()
    return render_template("carslist.html", cars = cars)
@carsales.route("/addcar", methods = ['GET','POST'])
def addcar():
    if request.method == 'GET':
        return render_template("addcar.html", car = {})
    if request.method == 'POST':
        id = int(request.form["id"])
        name = request.form["name"]
        year = int(request.form["year"])
        price = float(request.form["price"])
        conn = connection()
        cursor = conn.cursor()
        cursor.execute("INSERT INTO dbo.TblCars (id, name, year, price) VALUES (?, ?, ?, ?)", id, name, year, price)
        conn.commit()
        conn.close()
        return redirect('/')
@carsales.route('/updatecar/<int:id>',methods = ['GET','POST'])
def updatecar(id):
    cr = []
    conn = connection()
    cursor = conn.cursor()
    if request.method == 'GET':
        cursor.execute("SELECT * FROM dbo.TblCars WHERE id = ?", id)
        for row in cursor.fetchall():
            cr.append({"id": row[0], "name": row[1], "year": row[2], "price": row[3]})
        conn.close()
        return render_template("addcar.html", car = cr[0])
    if request.method == 'POST':
        name = str(request.form["name"])
        year = int(request.form["year"])
        price = float(request.form["price"])
        cursor.execute("UPDATE dbo.TblCars SET name = ?, year = ?, price = ? WHERE id = ?", name, year, price, id)
        conn.commit()
        conn.close()
        return redirect('/')
@carsales.route('/deletecar/<int:id>')
def deletecar(id):
    conn = connection()
    cursor = conn.cursor()
    cursor.execute("DELETE FROM dbo.TblCars WHERE id = ?", id)
    conn.commit()
    conn.close()
    return redirect('/')

if(__name__ == "__main__"):
    carsales.run()

<!DOCTYPE html>
<html lang="en-US" dir="ltr">
<head>
    <title>Cars List</title>
    
    <link rel="stylesheet" crossorigin="anonymous"
	href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" >
    
	<script crossorigin="anonymous"
	src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/js/bootstrap.bundle.min.js" >
	</script>

</head>

<body>
    <h2>Cars List</h2>
    <a class="btn btn-primary" href="addcar">Add New Car</a>
    <table class="table">
        <thead>
            <tr>
            <th scope="col">Id</th>
            <th scope="col">Name</th>
            <th scope="col">Year</th>
            <th scope="col">Price</th>
            <th scope="col">Edit</th>
            <th scope="col">Delete</th>
            </tr>
        </thead>
        <tbody>
            {% for car in cars %}
                <tr>
                    <td>{{ car.id }}</th>
                    <td>{{ car.name }}</td>
                    <td>{{ car.year }}</td>
                    <td>{{ car.price }}</td>
                    <td><a href='updatecar/{{ car.id }}'>Edit</a></td>
                    <td><a href='deletecar/{{ car.id }}'>Delete</a></td>
                </tr>
            {% endfor %}
        </tbody>
    </table>
</body>

<!DOCTYPE html>
<html lang="en-US" dir="ltr">
<head>
    <title>Car Details</title>
    
    <link rel="stylesheet" crossorigin="anonymous"
	href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" >
    
	<script crossorigin="anonymous"
	src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/js/bootstrap.bundle.min.js" >
	</script>

</head>

<body>
    <h2>Car Details</h2>

    <form action="" method = "POST">
        <div class="form-group row">
          <label for="id">Id</label>
          <input type="text" class="form-control" name="id" id="id" value="{{car.id}}">
        </div>
        <div class="form-group row">
            <label for="name">Maker and Model</label>
            <input type="text" class="form-control" name="name" id="name" value="{{car.name}}">
        </div>
        <div class="form-group row">
            <label for="year">Make Year</label>
            <input type="text" class="form-control" name="year" id="year" value="{{car.year}}">
        </div>
        <div class="form-group row">
            <label for="price">Sell Price</label>
            <input type="text" class="form-control" name="price" id="price" value="{{car.price}}">
        </div>
        <button type="btnAdd" class="btn btn-primary">Submit</button>
        <a href="/" class="btn btn-primary">Cancel</a>
      </form>
</body>

Other web app samples

Crud Samples implemented using different frameworks and databases.

Flask

Flask CRUD with JSON

Flask CRUD with SQL Server

Flask CRUD with MySQL

Flask Web App Sample using MongoDB

Flask CRUD with Oracle

Flask CRUD with PostgreSQL

Flask Web App Sample using MariaDB

Flask Web App Sample using Firebase DB

Django

Django CRUD with JSON

Django CRUD with SQL Server

Django CRUD with MySQL

Django Web App Sample using MongoDB

Django CRUD with Oracle

Django CRUD with PostgreSQL

Django Web App Sample using MariaDB

Django Web App Sample using Firebase DB

CherryPy

CherryPy CRUD with SQL Server

CherryPy Web App Sample using MongoDB

CherryPy CRUD with Oracle

CherryPy CRUD with JSON

CherryPy Web App Sample using Firebase DB

CherryPy CRUD with MySQL

CherryPy Web App Sample using MariaDB

CherryPy CRUD with PostgreSQL

Python Flask web application sample with SQL Server database

Contents

Install Python and setup Virtual Environment

Install pyodbc

pyodbc Installation Error - Microsoft Visual C++ 14.0 or greater is required

Install Flask

Initial steps for Flask Web Apps

Setting up First page

Database Setup

Fetch data from SQL Server DB and list

Insert new item to SQL Server DB

Update items - SQL Server DB

Delete an Item from SQL Server DB

Flask CRUD with SQL Server database - Complete code

Other web app samples

Flask

Django

CherryPy