Using JSON Type with Flask-sqlalchemy & Postgresql

Question

Background: I am building a Flask App and I have stored my data into a postgresql database and within a JSON column type.

Task: In my view functions, I would like to order a database query by {Key:Value} from JSON column

Accomplished: I have been successful in performing this query at the psql command-line by using the following command for example:

select * from target where cast(product->>'profit' as float) > 100 order by cast(product->>'salesrank' as integer) asc;

Problem: I can not replicate this query in my code (see code for Model below in Extra Info Section)

from app import app, db from models import Target   data = Target.query.order_by(Target.product['salesrank']) 

Error received - ProgrammingError: (ProgrammingError) could not identify an ordering operator for type json LINE 2: FROM target ORDER BY target.product -> 'salesrank' ^ HINT: Use an explicit ordering operator or modify the query. 'SELECT target.id AS target_id, target.store AS target_store, target.product AS target_product, target.asin AS target_asin, target.date AS target_date \nFROM target ORDER BY target.product -> %(product_1)s \n LIMIT %(param_1)s' {'product_1': 'salesrank', 'param_1': 1}

Extra Info My Target model was set up as such:

#models.py from app import db from sqlalchemy.dialects.postgresql import JSON import datetime  class Target(db.Model):     __tablename__ = 'target'      id = db.Column(db.Integer)     store = db.Column(db.String())     product = db.Column(JSON)     asin = db.Column(db.String(), primary_key=True)     date = db.Column(db.DateTime, default=datetime.datetime.utcnow()) 

My App.py file where I define Flask and Sqlalchemy

from flask import Flask import os from flask.ext.sqlalchemy import SQLAlchemy from flask_bootstrap import Bootstrap  app = Flask(__name__) app.config.from_object(os.environ['APP_SETTINGS']) db = SQLAlchemy(app) Bootstrap(app)  import views from app import app from models import Result  if __name__ == '__main__':     app.run(host='192.168.1.5', port=5000, debug=True) 

Thank you for any help you can provide!

Answer 1

Looking at the SQLAlchemy documentation for the JSON data type it appears that you should be able to use the .cast method:

from sqlalchemy.types import Integer  from app import app, db from models import Target   # SQLAlchemy 1.1+ data = Target.query.order_by(Target.product['salesrank'].astext.cast(Integer))  # SQLAlchemy < 1 data = Target.query.order_by(Target.product['salesrank'].cast(Integer))