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!

Asked By: larrywgray

||

Source

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))

Answered By: Sean Vieira

Using JSON Type with Flask-sqlalchemy & Postgresql

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