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Flask Graphene SQLAlchemy Tutorial

• Introduction
• Project set-up
• Create database
  • database.py
  • model_people.py
  • model_planet.py
  • setup.py
• Create GraphQL schemas
  • schema_people.py
  • schema_planet.py
  • schema.py

Introduction

The objective of this tutorial is to describe step by step how to create a GraphQL API using Python and more specifically the following packages:

• Flask
• Flask-SQLAlchemy
• SQLAlchemy
• Graphene

The API will expose data coming from an SQLite database stored locally on your machine. The end result will follow the files architecture described in the schema below. This files architecture as been reworked compared to previous tutorials I have followed on the topic with the intention to make it more scalable. It also contains complete examples of GraphQL mutations which I was not able to find in existing tutorials:

• The example folder contains the files used by Flask to start the API and the schema files used by Graphene to define GraphQL queries and mutations. It also contains the database sub folder.
• The database sub folder contains files used to create and interact with the SQLite database. It contains in particular one model file per database table which are mapped to SQLAlchemy classes.

Project set-up

Open a terminal to create your Python virtual environment. Keep the environment name short for convenience. I named it gql in the example below.

$ sudo apt-get install python3-venv
$ python3 -m venv /mypath/gql
$ source /mypath/gql/bin/activate

The last command above is used to activate your virtual environment. Once activated, install the required third party Python packages. I have specifically indicated the versions I used for this tutorial.

$ pip3 install sqlalchemy==1.1.14
$ pip3 install graphene==2.0.0
$ pip3 install graphene-sqlalchemy==2.0.0
$ pip3 install flask==0.11.1

$ cd flask-graphene-sqlalchemy
$ pip3 install -r requirements.txt

Create a new folder for your project, I named it "example"

Create database

The database will contain some Planet and People data from Star Wars, stored in 2 different tables (data source: The Star Wars API):

• Planet: List of planets appearing in Star Wars movies
• People: List of people appearing in Star Wars movies

Note there is a relationship between planets and people as one planet is the homeworld of one or several persons in the people table. It is a "one-to-many" relationship (one planet, many people). The homeworld column in the people table will be used as foreign key of the planet and as such will contain the planet id.

In your project folder create a sub folder named database. In the database sub folder create a file named database.py. This file will be used by SQLALchemy to:

• Define the database engine used to generate and interact with the SQLite file named database.db.
• Create the Base class used to produce database tables and map them to their respective classes and attributes.
• Manage the database sessions in order to execute queries against the database.

database.py

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import scoped_session, sessionmaker
import os

# Create database engine
db_name = 'database.db'
db_path = os.path.join(os.path.dirname(__file__), db_name)
db_uri = 'sqlite:///{}'.format(db_path)
engine = create_engine(db_uri, convert_unicode=True)

# Declarative base model to create database tables and classes
Base = declarative_base()
Base.metadata.bind = engine  # Bind engine to metadata of the base class

# Create database session object
db_session = scoped_session(sessionmaker(bind=engine, expire_on_commit=False))
Base.query = db_session.query_property()  # Used by graphql to execute queries

In the database sub folder create two files named model_people.py and model_planet.py which will contain the data model information required by SQLAlchemy to create the tables and relationships.

model_people.py

from .database import Base
from sqlalchemy import Column, ForeignKey, Integer, String


class People(Base):
    """People model."""

    __tablename__ = 'people'

    id = Column('id', Integer, primary_key=True)
    name = Column('name', String)
    height = Column('height', Integer)
    mass = Column('mass', Integer)
    hair_color = Column('hair_color', String)
    skin_color = Column('skin_color', String)
    eye_color = Column('eye_color', String)
    birth_year = Column('birth_year', String)
    gender = Column('gender', String)
    homeworld = Column('homeworld', Integer, ForeignKey('planet.id'))
    created = Column('created', String)
    edited = Column('edited', String)
    url = Column('url', String)

model_planet.py

from .database import Base
from sqlalchemy import Column, Integer, String
from sqlalchemy.orm import relationship


class Planet(Base):
    """Planet model."""

    __tablename__ = 'planet'

    id = Column('id', Integer, primary_key=True)
    name = Column('name', String)
    rotation_period = Column('rotation_period', Integer)
    orbital_period = Column('orbital_period', Integer)
    diameter = Column('diameter', Integer)
    climate = Column('climate', String)
    gravity = Column('gravity', String)
    terrain = Column('terrain', String)
    surface_water = Column('surface_water', Integer)
    population = Column('population', Integer)
    created = Column('created', String)
    edited = Column('edited', String)
    url = Column('url', String)

    peoples = relationship('People', backref='planet')

setup.py

from ast import literal_eval
from database import database
from database import model_people
from database import model_planet
import logging
import sys

# Load logging configuration
log = logging.getLogger(__name__)
logging.basicConfig(
    stream=sys.stdout,
    level=logging.INFO,
    format='%(asctime)s - %(name)s - %(levelname)s - %(message)s')


if __name__ == '__main__':
    log.info('Create database {}'.format(database.db_name))
    database.Base.metadata.create_all(database.engine)

    log.info('Insert Planet data in database')
    with open('database/data/planet.json', 'r') as file:
        data = literal_eval(file.read())
        for record in data:
            # Extract planet id from url
            record['id'] = record['url'][record['url'].index('https://swapi.co/api/planets/')+29:-1]
            planet = model_planet.Planet(**record)
            database.db_session.add(planet)
        database.db_session.commit()

    log.info('Insert People data in database')
    with open('database/data/people.json', 'r') as file:
        data = literal_eval(file.read())
        for record in data:
            # Extract people and planet id from urls
            record['id'] = record['url'][record['url'].index('https://swapi.co/api/people/')+28:-1]
            record['homeworld'] = record['homeworld'][record['homeworld'].index('https://swapi.co/api/planets/')+29:-1]
            planet = model_people.People(**record)
            database.db_session.add(planet)
        database.db_session.commit()

Create GraphQL schemas

schema_people.py

schema_planet.py

schema.py