Building a CRUD Application with Flask and SQLAlchemy

0398

CRUD Applications (5 Part Series)

1 Building a CRUD Application with Node.js, Express, and MongoDB
2 Building a CRUD Application with Node.js, Express, and MySQL
3 Building a CRUD Application with NestJS and MongoDB
4 Building a CRUD Application with Flask and SQLAlchemy
5 Building a CRUD Application with Flask and MongoDB

In this blog, we’ll walk through building a simple CRUD (Create, Read, Update, Delete) API using Flask and SQLAlchemy. This guide will cover setting up the project, configuring the database, defining models, creating routes, and running the application.

Prerequisites

Before getting started, ensure you have the following installed:

  • Python 3.x
  • Flask
  • Flask-SQLAlchemy
  • Flask-Migrate

Project Setup

1. Clone the Repository 

git clone https://github.com/manthanank/crud-flask-sqlalchemy.git
<span>cd </span>crud-flask
git clone https://github.com/manthanank/crud-flask-sqlalchemy.git
<span>cd </span>crud-flask
git clone https://github.com/manthanank/crud-flask-sqlalchemy.git
cd crud-flask

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2. Create a Virtual Environment 

python <span>-m</span> venv venv
<span>source </span>venv/bin/activate  <span># On Windows: `venv\Scripts\activate`</span>
python <span>-m</span> venv venv
<span>source </span>venv/bin/activate  <span># On Windows: `venv\Scripts\activate`</span>
python -m venv venv
source venv/bin/activate  # On Windows: `venv\Scripts\activate`

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3. Install Dependencies 

pip <span>install</span> <span>-r</span> requirements.txt
pip <span>install</span> <span>-r</span> requirements.txt
pip install -r requirements.txt

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Database Configuration

We are using Flask-SQLAlchemy for ORM and Flask-Migrate for database migrations. The database configuration is stored in app/config.py: 

<span>import</span> <span>os</span>
<span>from</span> <span>dotenv</span> <span>import</span> <span>load_dotenv</span>
<span>load_dotenv</span><span>()</span>
<span>class</span> <span>Config</span><span>:</span>
    <span>SQLALCHEMY_DATABASE_URI</span> <span>=</span> <span>os</span><span>.</span><span>getenv</span><span>(</span><span>"</span><span>DATABASE_URL</span><span>"</span><span>,</span> <span>"</span><span>sqlite:///app.db</span><span>"</span><span>)</span>
    <span>SQLALCHEMY_TRACK_MODIFICATIONS</span> <span>=</span> <span>False</span>
<span>import</span> <span>os</span>
<span>from</span> <span>dotenv</span> <span>import</span> <span>load_dotenv</span>

<span>load_dotenv</span><span>()</span>

<span>class</span> <span>Config</span><span>:</span>
    <span>SQLALCHEMY_DATABASE_URI</span> <span>=</span> <span>os</span><span>.</span><span>getenv</span><span>(</span><span>"</span><span>DATABASE_URL</span><span>"</span><span>,</span> <span>"</span><span>sqlite:///app.db</span><span>"</span><span>)</span>
    <span>SQLALCHEMY_TRACK_MODIFICATIONS</span> <span>=</span> <span>False</span>
import os
from dotenv import load_dotenv

load_dotenv()

class Config:
    SQLALCHEMY_DATABASE_URI = os.getenv("DATABASE_URL", "sqlite:///app.db")
    SQLALCHEMY_TRACK_MODIFICATIONS = False

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Initializing the Database

To set up the database, run the following commands: 

flask db init
flask db migrate <span>-m</span> <span>"Initial migration"</span>
flask db upgrade
flask db init
flask db migrate <span>-m</span> <span>"Initial migration"</span>
flask db upgrade
flask db init
flask db migrate -m "Initial migration"
flask db upgrade

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On Windows, before running these commands, set the environment variable: 

<span>set </span><span>FLASK_APP</span><span>=</span>run.py
<span>set </span><span>FLASK_APP</span><span>=</span>run.py
set FLASK_APP=run.py

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Defining the Model

We define a simple Item model in app/models.py: 

<span>from</span> <span>app</span> <span>import</span> <span>db</span>
<span>class</span> <span>Item</span><span>(</span><span>db</span><span>.</span><span>Model</span><span>):</span>
    <span>id</span> <span>=</span> <span>db</span><span>.</span><span>Column</span><span>(</span><span>db</span><span>.</span><span>Integer</span><span>,</span> <span>primary_key</span><span>=</span><span>True</span><span>)</span>
    <span>name</span> <span>=</span> <span>db</span><span>.</span><span>Column</span><span>(</span><span>db</span><span>.</span><span>String</span><span>(</span><span>100</span><span>),</span> <span>nullable</span><span>=</span><span>False</span><span>)</span>
    <span>description</span> <span>=</span> <span>db</span><span>.</span><span>Column</span><span>(</span><span>db</span><span>.</span><span>String</span><span>(</span><span>200</span><span>))</span>
    <span>def</span> <span>to_dict</span><span>(</span><span>self</span><span>):</span>
        <span>return</span> <span>{</span><span>"</span><span>id</span><span>"</span><span>:</span> <span>self</span><span>.</span><span>id</span><span>,</span> <span>"</span><span>name</span><span>"</span><span>:</span> <span>self</span><span>.</span><span>name</span><span>,</span> <span>"</span><span>description</span><span>"</span><span>:</span> <span>self</span><span>.</span><span>description</span><span>}</span>
<span>from</span> <span>app</span> <span>import</span> <span>db</span>

<span>class</span> <span>Item</span><span>(</span><span>db</span><span>.</span><span>Model</span><span>):</span>
    <span>id</span> <span>=</span> <span>db</span><span>.</span><span>Column</span><span>(</span><span>db</span><span>.</span><span>Integer</span><span>,</span> <span>primary_key</span><span>=</span><span>True</span><span>)</span>
    <span>name</span> <span>=</span> <span>db</span><span>.</span><span>Column</span><span>(</span><span>db</span><span>.</span><span>String</span><span>(</span><span>100</span><span>),</span> <span>nullable</span><span>=</span><span>False</span><span>)</span>
    <span>description</span> <span>=</span> <span>db</span><span>.</span><span>Column</span><span>(</span><span>db</span><span>.</span><span>String</span><span>(</span><span>200</span><span>))</span>

    <span>def</span> <span>to_dict</span><span>(</span><span>self</span><span>):</span>
        <span>return</span> <span>{</span><span>"</span><span>id</span><span>"</span><span>:</span> <span>self</span><span>.</span><span>id</span><span>,</span> <span>"</span><span>name</span><span>"</span><span>:</span> <span>self</span><span>.</span><span>name</span><span>,</span> <span>"</span><span>description</span><span>"</span><span>:</span> <span>self</span><span>.</span><span>description</span><span>}</span>
from app import db

class Item(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(100), nullable=False)
    description = db.Column(db.String(200))

    def to_dict(self):
        return {"id": self.id, "name": self.name, "description": self.description}

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Creating the API Routes

In app/routes.py, we define the API endpoints for CRUD operations using Flask’s Blueprints:

1. Create an Item 

<span>@api_bp.route</span><span>(</span><span>"</span><span>/items</span><span>"</span><span>,</span> <span>methods</span><span>=</span><span>[</span><span>"</span><span>POST</span><span>"</span><span>])</span>
<span>def</span> <span>create_item</span><span>():</span>
    <span>data</span> <span>=</span> <span>request</span><span>.</span><span>json</span>
    <span>new_item</span> <span>=</span> <span>Item</span><span>(</span><span>name</span><span>=</span><span>data</span><span>[</span><span>"</span><span>name</span><span>"</span><span>],</span> <span>description</span><span>=</span><span>data</span><span>.</span><span>get</span><span>(</span><span>"</span><span>description</span><span>"</span><span>))</span>
    <span>db</span><span>.</span><span>session</span><span>.</span><span>add</span><span>(</span><span>new_item</span><span>)</span>
    <span>db</span><span>.</span><span>session</span><span>.</span><span>commit</span><span>()</span>
    <span>return</span> <span>jsonify</span><span>(</span><span>new_item</span><span>.</span><span>to_dict</span><span>()),</span> <span>201</span>
<span>@api_bp.route</span><span>(</span><span>"</span><span>/items</span><span>"</span><span>,</span> <span>methods</span><span>=</span><span>[</span><span>"</span><span>POST</span><span>"</span><span>])</span>
<span>def</span> <span>create_item</span><span>():</span>
    <span>data</span> <span>=</span> <span>request</span><span>.</span><span>json</span>
    <span>new_item</span> <span>=</span> <span>Item</span><span>(</span><span>name</span><span>=</span><span>data</span><span>[</span><span>"</span><span>name</span><span>"</span><span>],</span> <span>description</span><span>=</span><span>data</span><span>.</span><span>get</span><span>(</span><span>"</span><span>description</span><span>"</span><span>))</span>
    <span>db</span><span>.</span><span>session</span><span>.</span><span>add</span><span>(</span><span>new_item</span><span>)</span>
    <span>db</span><span>.</span><span>session</span><span>.</span><span>commit</span><span>()</span>
    <span>return</span> <span>jsonify</span><span>(</span><span>new_item</span><span>.</span><span>to_dict</span><span>()),</span> <span>201</span>
@api_bp.route("/items", methods=["POST"])
def create_item():
    data = request.json
    new_item = Item(name=data["name"], description=data.get("description"))
    db.session.add(new_item)
    db.session.commit()
    return jsonify(new_item.to_dict()), 201

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2. Retrieve All Items 

<span>@api_bp.route</span><span>(</span><span>"</span><span>/items</span><span>"</span><span>,</span> <span>methods</span><span>=</span><span>[</span><span>"</span><span>GET</span><span>"</span><span>])</span>
<span>def</span> <span>get_items</span><span>():</span>
    <span>items</span> <span>=</span> <span>Item</span><span>.</span><span>query</span><span>.</span><span>all</span><span>()</span>
    <span>return</span> <span>jsonify</span><span>([</span><span>item</span><span>.</span><span>to_dict</span><span>()</span> <span>for</span> <span>item</span> <span>in</span> <span>items</span><span>])</span>
<span>@api_bp.route</span><span>(</span><span>"</span><span>/items</span><span>"</span><span>,</span> <span>methods</span><span>=</span><span>[</span><span>"</span><span>GET</span><span>"</span><span>])</span>
<span>def</span> <span>get_items</span><span>():</span>
    <span>items</span> <span>=</span> <span>Item</span><span>.</span><span>query</span><span>.</span><span>all</span><span>()</span>
    <span>return</span> <span>jsonify</span><span>([</span><span>item</span><span>.</span><span>to_dict</span><span>()</span> <span>for</span> <span>item</span> <span>in</span> <span>items</span><span>])</span>
@api_bp.route("/items", methods=["GET"])
def get_items():
    items = Item.query.all()
    return jsonify([item.to_dict() for item in items])

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3. Retrieve a Single Item 

<span>@api_bp.route</span><span>(</span><span>"</span><span>/items/<int:item_id></span><span>"</span><span>,</span> <span>methods</span><span>=</span><span>[</span><span>"</span><span>GET</span><span>"</span><span>])</span>
<span>def</span> <span>get_item</span><span>(</span><span>item_id</span><span>):</span>
    <span>item</span> <span>=</span> <span>Item</span><span>.</span><span>query</span><span>.</span><span>get_or_404</span><span>(</span><span>item_id</span><span>)</span>
    <span>return</span> <span>jsonify</span><span>(</span><span>item</span><span>.</span><span>to_dict</span><span>())</span>
<span>@api_bp.route</span><span>(</span><span>"</span><span>/items/<int:item_id></span><span>"</span><span>,</span> <span>methods</span><span>=</span><span>[</span><span>"</span><span>GET</span><span>"</span><span>])</span>
<span>def</span> <span>get_item</span><span>(</span><span>item_id</span><span>):</span>
    <span>item</span> <span>=</span> <span>Item</span><span>.</span><span>query</span><span>.</span><span>get_or_404</span><span>(</span><span>item_id</span><span>)</span>
    <span>return</span> <span>jsonify</span><span>(</span><span>item</span><span>.</span><span>to_dict</span><span>())</span>
@api_bp.route("/items/<int:item_id>", methods=["GET"])
def get_item(item_id):
    item = Item.query.get_or_404(item_id)
    return jsonify(item.to_dict())

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4. Update an Item 

<span>@api_bp.route</span><span>(</span><span>"</span><span>/items/<int:item_id></span><span>"</span><span>,</span> <span>methods</span><span>=</span><span>[</span><span>"</span><span>PUT</span><span>"</span><span>])</span>
<span>def</span> <span>update_item</span><span>(</span><span>item_id</span><span>):</span>
    <span>item</span> <span>=</span> <span>Item</span><span>.</span><span>query</span><span>.</span><span>get_or_404</span><span>(</span><span>item_id</span><span>)</span>
    <span>data</span> <span>=</span> <span>request</span><span>.</span><span>json</span>
    <span>item</span><span>.</span><span>name</span> <span>=</span> <span>data</span><span>.</span><span>get</span><span>(</span><span>"</span><span>name</span><span>"</span><span>,</span> <span>item</span><span>.</span><span>name</span><span>)</span>
    <span>item</span><span>.</span><span>description</span> <span>=</span> <span>data</span><span>.</span><span>get</span><span>(</span><span>"</span><span>description</span><span>"</span><span>,</span> <span>item</span><span>.</span><span>description</span><span>)</span>
    <span>db</span><span>.</span><span>session</span><span>.</span><span>commit</span><span>()</span>
    <span>return</span> <span>jsonify</span><span>(</span><span>item</span><span>.</span><span>to_dict</span><span>())</span>
<span>@api_bp.route</span><span>(</span><span>"</span><span>/items/<int:item_id></span><span>"</span><span>,</span> <span>methods</span><span>=</span><span>[</span><span>"</span><span>PUT</span><span>"</span><span>])</span>
<span>def</span> <span>update_item</span><span>(</span><span>item_id</span><span>):</span>
    <span>item</span> <span>=</span> <span>Item</span><span>.</span><span>query</span><span>.</span><span>get_or_404</span><span>(</span><span>item_id</span><span>)</span>
    <span>data</span> <span>=</span> <span>request</span><span>.</span><span>json</span>
    <span>item</span><span>.</span><span>name</span> <span>=</span> <span>data</span><span>.</span><span>get</span><span>(</span><span>"</span><span>name</span><span>"</span><span>,</span> <span>item</span><span>.</span><span>name</span><span>)</span>
    <span>item</span><span>.</span><span>description</span> <span>=</span> <span>data</span><span>.</span><span>get</span><span>(</span><span>"</span><span>description</span><span>"</span><span>,</span> <span>item</span><span>.</span><span>description</span><span>)</span>
    <span>db</span><span>.</span><span>session</span><span>.</span><span>commit</span><span>()</span>
    <span>return</span> <span>jsonify</span><span>(</span><span>item</span><span>.</span><span>to_dict</span><span>())</span>
@api_bp.route("/items/<int:item_id>", methods=["PUT"])
def update_item(item_id):
    item = Item.query.get_or_404(item_id)
    data = request.json
    item.name = data.get("name", item.name)
    item.description = data.get("description", item.description)
    db.session.commit()
    return jsonify(item.to_dict())

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5. Delete an Item 

<span>@api_bp.route</span><span>(</span><span>"</span><span>/items/<int:item_id></span><span>"</span><span>,</span> <span>methods</span><span>=</span><span>[</span><span>"</span><span>DELETE</span><span>"</span><span>])</span>
<span>def</span> <span>delete_item</span><span>(</span><span>item_id</span><span>):</span>
    <span>item</span> <span>=</span> <span>Item</span><span>.</span><span>query</span><span>.</span><span>get_or_404</span><span>(</span><span>item_id</span><span>)</span>
    <span>db</span><span>.</span><span>session</span><span>.</span><span>delete</span><span>(</span><span>item</span><span>)</span>
    <span>db</span><span>.</span><span>session</span><span>.</span><span>commit</span><span>()</span>
    <span>return</span> <span>jsonify</span><span>({</span><span>"</span><span>message</span><span>"</span><span>:</span> <span>"</span><span>Item deleted successfully</span><span>"</span><span>})</span>
<span>@api_bp.route</span><span>(</span><span>"</span><span>/items/<int:item_id></span><span>"</span><span>,</span> <span>methods</span><span>=</span><span>[</span><span>"</span><span>DELETE</span><span>"</span><span>])</span>
<span>def</span> <span>delete_item</span><span>(</span><span>item_id</span><span>):</span>
    <span>item</span> <span>=</span> <span>Item</span><span>.</span><span>query</span><span>.</span><span>get_or_404</span><span>(</span><span>item_id</span><span>)</span>
    <span>db</span><span>.</span><span>session</span><span>.</span><span>delete</span><span>(</span><span>item</span><span>)</span>
    <span>db</span><span>.</span><span>session</span><span>.</span><span>commit</span><span>()</span>
    <span>return</span> <span>jsonify</span><span>({</span><span>"</span><span>message</span><span>"</span><span>:</span> <span>"</span><span>Item deleted successfully</span><span>"</span><span>})</span>
@api_bp.route("/items/<int:item_id>", methods=["DELETE"])
def delete_item(item_id):
    item = Item.query.get_or_404(item_id)
    db.session.delete(item)
    db.session.commit()
    return jsonify({"message": "Item deleted successfully"})

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Setup Environment Variables

.env 

DATABASE_URL=sqlite:///app.db
DATABASE_URL=sqlite:///app.db
DATABASE_URL=sqlite:///app.db

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Running the Application

Run the Flask application with: 

python run.py
python run.py
python run.py

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The API will be accessible at http://127.0.0.1:5000/api/items.

API Endpoints

Method Endpoint Description
POST /api/items Create a new item
GET /api/items Get all items
GET /api/items/<id> Get a single item
PUT /api/items/<id> Update an item
DELETE /api/items/<id> Delete an item

Testing the API

You can test the API using Postman or cURL.

  • Create an Item: 
  curl <span>-X</span> POST http://127.0.0.1:5000/api/items <span>-H</span> <span>"Content-Type: application/json"</span> <span>-d</span> <span>'{"name": "Laptop", "description": "Gaming laptop"}'</span>
  curl <span>-X</span> POST http://127.0.0.1:5000/api/items <span>-H</span> <span>"Content-Type: application/json"</span> <span>-d</span> <span>'{"name": "Laptop", "description": "Gaming laptop"}'</span>
  curl -X POST http://127.0.0.1:5000/api/items -H "Content-Type: application/json" -d '{"name": "Laptop", "description": "Gaming laptop"}'

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  • Get All Items: 
  curl <span>-X</span> GET http://127.0.0.1:5000/api/items
  curl <span>-X</span> GET http://127.0.0.1:5000/api/items
  curl -X GET http://127.0.0.1:5000/api/items

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  • Get a Specific Item: 
  curl <span>-X</span> GET http://127.0.0.1:5000/api/items/1
  curl <span>-X</span> GET http://127.0.0.1:5000/api/items/1
  curl -X GET http://127.0.0.1:5000/api/items/1

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  • Update an Item: 
  curl <span>-X</span> PUT http://127.0.0.1:5000/api/items/1 <span>-H</span> <span>"Content-Type: application/json"</span> <span>-d</span> <span>'{"name": "Updated Laptop", "description": "High-performance gaming laptop"}'</span>
  curl <span>-X</span> PUT http://127.0.0.1:5000/api/items/1 <span>-H</span> <span>"Content-Type: application/json"</span> <span>-d</span> <span>'{"name": "Updated Laptop", "description": "High-performance gaming laptop"}'</span>
  curl -X PUT http://127.0.0.1:5000/api/items/1 -H "Content-Type: application/json" -d '{"name": "Updated Laptop", "description": "High-performance gaming laptop"}'

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  • Delete an Item: 
  curl <span>-X</span> DELETE http://127.0.0.1:5000/api/items/1
  curl <span>-X</span> DELETE http://127.0.0.1:5000/api/items/1
  curl -X DELETE http://127.0.0.1:5000/api/items/1

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Conclusion

In this guide, we built a Flask CRUD API using SQLAlchemy for database operations and Flask-Migrate for migrations. This setup provides a solid foundation for building RESTful services in Flask.

Congratulations! You’ve built a Flask CRUD API with SQLAlchemy.

Happy coding!

Exploring the Code

Visit the GitHub repository to explore the code in detail.

CRUD Applications (5 Part Series)

1 Building a CRUD Application with Node.js, Express, and MongoDB
2 Building a CRUD Application with Node.js, Express, and MySQL
3 Building a CRUD Application with NestJS and MongoDB
4 Building a CRUD Application with Flask and SQLAlchemy
5 Building a CRUD Application with Flask and MongoDB

原文链接：Building a CRUD Application with Flask and SQLAlchemy

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Vito的头像-拾光赋

Vito5个月前2

你就是我心中的那首忐忑，总是让我惊心动魄
Jason.Meng的头像-拾光赋钻石会员

Jason.Meng徽章-人气大使-拾光赋5个月前2

总是会在人生的不同阶段反复爱上大佬的文章~
每日一言
pencil and a dream can take you anywhere.
拿起笔，写下你的梦想，你的人生就从此刻起航