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Flask Marshmallow Flask with SQLAlchemy & Marshmallow

Md. Nahidur Rahman
Software Engineer
・4 min read

Flask with SQLAlchemy & Marshmallow

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In the article we will build a simple REST API using Flask, SQLAlchemy and Marshmallow. We will be building a note taking application where these two API endpoints /note/ and /note/<id>/ will be available.

We will be able to create new note or get all the notes by doing a POST or a GET request to /note/ api endpoint. Not only that we will be able to get the details of the note or update the note or delete the note with a GET or a PATCH or a DELETE request to /note/<id>/ api endpoint.

First of all, we will give a brief descriptions of the libraries that we will be using in this article.

Flask is a lightweight WSGI web application framework in Python. It is designed to make getting started very quickly and very easily.

marshmallow is an ORM/ODM/framework-agnostic library for converting complex datatypes, such as objects, to and from native Python datatypes.

Flask-Marshmallow is a thin integration layer for Flask and marshmallow that adds additional features to marshmallow.

SQLAlchemy is the Python SQL toolkit and Object Relational Mapper that gives application developers the full power and flexibility of SQL.

Flask-SQLAlchemy is an extension for Flask that adds support for SQLAlchemy to your application. It aims to simplify using SQLAlchemy with Flask.

marshmallow-sqlalchemy An SQLAlchemy integration with the marshmallow (de)serialization library.

We will be using pipenv as our dependency manager. We are assuming that pipenv is already installed in your system.

Follow the steps bellow and at the end you will have a simple note application running on http://localhost:5000/.

Step 1: Setup Project Environment

pipenv --three
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Step 2: Install Flask and Other Dependencies

Run the following commands to install all the dependencies including Flask.

pipenv install flask
pipenv install flask-marshmallow
pipenv install flask-sqlalchemy
pipenv install marshmallow-sqlalchemy
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After running those commands marshmallow and SQLAlchemy will be installed internally as dependency.

Step 3: Create app.py File

touch app.py
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Step 4: Add This Code to app.py File

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello, World!'

if __name__ == '__main__':
    app.run(debug=True)    
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Step 5: Start pipenv Shell

pipenv shell
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Step 6: Run Flask Server

python app.py
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Step 7: Go to the Browser

Start your favorite browser and go to the http://localhost:5000/ url and you will see "Hello, World!" printed.

Step 8: Integrate SQLAlchemy & Marshmallow

Add the following imports into the app.py file.

import os
from flask_sqlalchemy import SQLAlchemy
from flask_marshmallow import Marshmallow
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And add the following code after the creation of Flask app instance.

basedir = os.path.abspath(os.path.dirname(__file__))
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///'+ \
                os.path.join(basedir, 'db.sqlite3')

db = SQLAlchemy(app)
ma = Marshmallow(app)
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Step 9: Create Model

Declare the model like following.

class NoteModel(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(100))
    content = db.Column(db.String(255))

    def __init__(self, title, content):
        self.title = title
        self.content = content
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Step 10: Create Schema

Generate marshmallow schema from the model.

class NoteSchema(ma.SQLAlchemyAutoSchema):
    class Meta:
        model = NoteModel
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Step 11: Build Out API Actions

@app.route('/note/')
def note_list():
    all_notes = NoteModel.query.all()
    return jsonify(notes_schema.dump(all_notes))


@app.route('/note/', methods=['POST'])
def create_note():
    title = request.json.get('title', '')
    content = request.json.get('content', '')

    note = NoteModel(title=title, content=content)

    db.session.add(note)
    db.session.commit()

    return note_schema.jsonify(note)


@app.route('/note/<int:note_id>/', methods=["GET"])
def note_detail(note_id):
    note = NoteModel.query.get(note_id)
    return note_schema.jsonify(note)


@app.route('/note/<int:note_id>/', methods=['PATCH'])
def update_note(note_id):
    title = request.json.get('title', '')
    content = request.json.get('content', '')

    note = NoteModel.query.get(note_id)

    note.title = title
    note.content = content

    db.session.add(note)
    db.session.commit()

    return note_schema.jsonify(note)


@app.route('/note/<int:note_id>/', methods=["DELETE"])
def delete_note(note_id):
    note = NoteModel.query.get(note_id)

    db.session.delete(note)
    db.session.commit()

    return note_schema.jsonify(note)
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Step 12: Setup Database

Enter in python shell

python

>> from app import db
>> db.create_all()
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Step 13: Test APIs

We can use the tool Postman to test our APIs. But before that please ensure your development server is up and running using this command python app.py from Step 6.

Flask with SQLAlchemy & Marshmallow

The complete code of this article can be found on this repository.

This article is also published on nahidsaikat.com.

Discussion (6)

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agathver profile image
Amitosh Swain Mahapatra

Instead of this:

title = request.json.get('title', '')
content = request.json.get('content', '')
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You could use note_schema.load() to directly load request.json to marshmallow as well

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nahidsaikat profile image
Md. Nahidur Rahman Author

Yes, that will be better I think.

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msoutopico profile image
Manuel Souto Pico

Thanks for this tutorial. You don't know about the module flask-restful. I'd be curious to understand whether how what you do in this tutorial with marshmallow compares to how it would be done with flask-restful. Thanks.

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msoutopico profile image
Manuel Souto Pico

What is the part of your code that specifies the table in the database?

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codingsafari profile image
Nico Braun

What is the benefit of adding two ORMs? Can't you don't with flask and let's say sqlalchemy alone.

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nahidsaikat profile image
Md. Nahidur Rahman Author

There is not two ORMs, SQLAlchemy is the ORM but marshmallow is simplified object (de)serializer.

I used SQLAlchemy to handle DB things and marshmallow for the data serialization/de-serialization things.

You can learn more from their website, sqlalchemy.org/ marshmallow.readthedocs.io/en/stable/