alpersonalwebsite / flask-sql-data-modeling

Under development > flask-sql-data-modeling

Flask and SQL Data Modeling

Under Development

Overview

This is an easy, basic and raw example of HOW to model data with SQLAlchemy.

I'm including and extras folder with basic variations:

• PSQL
• psycopg2
• psycopg2 and SQLAlchemy
• psycopg2 and SQLAlchemy with SQL Expression
• psycopg2 and SQLAlchemy ORM

It purpose is merely educational

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Requirements

• Python 3.6+
• pip 3
• virtualenv
• psycopg2-binary
• SQLAlchemy
• PostgreSQL
• psql
• Flask
• Flask-Migrate

Local development

Install virtualenv

Install virtualenv to create isolated Python environments

pip3 install virtualenv

Initialize and activate a virtualenv

python3 -m virtualenv env
source env/bin/activate

After this step, you can use just python (instead of python3; same for pip)

Install dependencies

pip install -r requirements.txt

Create database

createdb agency

Run the setup script

source setup.sh

Running the server

With Flask

flask run --reload

Note: If you want to make your server publicly available add the flag: --host=0.0.0.0

flask run --reload --host=0.0.0.0

With Python

python src/app.py 

Note:

• When we run our application with flask the name of the app will be the name of our server file without the .py extension, in this case, app.
• When we run the script with python, python will assign the name of __main__ to the script when the script is executed.

So if you look at the end of our server file, src/app.py:

if __name__ == '__main__':
  app.run()

... since name is __main__, the app.run() is executed.

Populate data

psql agency

Linting

We are going to use pycodestyle to check for pep8 issues and autope8 to help us fix some of those issues.

If you don't have these packages, please, install them.

pip install pycodestyle
pip install autopep8

Then, at the root level:

pycodestyle src/

The output, in case of linting errors, would look like:

src/models.py:88:1: W293 blank line contains whitespace
src/models.py:89:3: E111 indentation is not a multiple of four
src/models.py:92:3: E111 indentation is not a multiple of four
src/models.py:97:6: W292 no newline at end of file

Now, you can use autopep8 to start fixing some violations.

autopep8 --in-place --aggressive --aggressive src/models.py

---

Notes:

PSQL: Create table and persist data

Drop and create the DB test, using the PostgreSQL cli.

dropdb test && createdb test

Then:

createdb test

psql test

CREATE TABLE my_tests (
  id INTEGER PRIMARY KEY,
  completed BOOLEAN NOT NULL DEFAULT False
);

INSERT INTO my_tests (id, completed) VALUES (1, False);

SELECT * FROM my_tests;

// Optional: delete db
dropdb test

Sample output:

 id | completed 
----+-----------
  1 | f
(1 row)

psycopg2: Create table and persist data

BE SURE you are not naming your file psycopg2.py our you will end importing our script instead of the psycopg2 module

Drop and create the DB test, using the PostgreSQL cli.

dropdb test && createdb test

Then:

python extras/psycopg2-sample.py

Sample output:

[(1, False)]

If you want to use string interpolation to compose your SQL query...

# Original
cursor.execute('INSERT INTO my_tests (id, completed) VALUES (1, False);')

# Example 1: %s and tuple
cursor.execute('INSERT INTO my_tests (id, completed) VALUES (%s, %s);', (1, False))

# Example 2: %(my_dic_key) and dictionary
SQL = 'INSERT INTO my_tests (id, completed) VALUES (%(id)s, %(completed)s);'

data = {
  'id': 1,
  'completed': False
}
cursor.execute(SQL, data)

psycopg2 and SQLAlchemy: Create table and persist data

python extras/psycopg2-and-sqlalchemy.py

Sample output:

[(1, False)]

psycopg2 and SQLAlchemy with SQL Expression: Create table and persist data

python extras/psycopg2-sqlalchemy-and-sql-expressions.py

Sample output:

[(1, False)]

psycopg2 and SQLAlchemy ORM: Create table and persist data

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Kudos

Extended version of Udacity's FSN SQL Data Modeling