How to get SQLAlchemy working with mysql with existing database

Question

I have problems operating with the exiting database in mysql using a sqlalchemy as I need it for building Flask RESTful api.

I get funny errors about circular dependencies here:

from flask import Flask, request, jsonify, make_response
from flaskext.mysql import MySQL
from flask_sqlalchemy import SQLAlchemy

#from webapi import models

# mysql = MySQL()
app = Flask(__name__)
app.config['SECRET_KEY'] = 'secretkey' #for use later
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://user:[email protected]/mydb'

db = SQLAlchemy(app)

class Extensions(db.Model):

    __tablename__ = "Extensions"

    extnbr = db.Column(db.Integer, primary_key=True, default="NULL")
    authname = db.Column(db.String(256), nullable=True, default="@nobody")
    extpriority = db.Column(db.Integer, nullable=True, default=0)
    callaccess = db.Column(db.Integer, nullable=True, default=0)
    extlocation = db.Column(db.String, nullable=True, default="NULL")
    display = db.Column(db.String, nullable=True, default="NULL")

@app.route("/")
def hello():
    return "Welcome to Python Flask App!"

@app.route("/extensions", methods=["GET"])
def get_all_extensions():
    users = Extensions.query.all()

    output = []

    for user in users:
      user_data = {}
      user_data['extnbr'] = user.extnbr
      user_data['authname'] = user.authname
      user_data['extpriority'] = user.extpriority
      user_data['callaccess'] = user.callaccess
      user_data['extlocation'] = user.extlocation
      user_data['display'] = user.display
      output.append({'extensions' : output})

    return jsonify({'users' : output})

if __name__ == "__main__":
    app.run(debug=True)

I get error about circular dependence:

Debug and trace:

https://dpaste.de/F3uX

Since you're not using from flaskext.mysql import MySQL for now, delete the line and see if it still occurs. — Joost
– Joost, Commented Apr 21, 2018 at 10:12
here is a full trace of error @Joost with SQLALCHEMY_ECHO = True dpaste.de/F3uX — MarkoShiva
– MarkoShiva, Commented Apr 21, 2018 at 10:36

Joost · Accepted Answer · 2018-04-21 10:48:35Z

1

This has to do with your output. You're appending a dictionary containing output to output itself, creating a funky data structure causing the json error.

Try changing

 output.append({'extensions' : output})

to this:

output.append({'extensions' : user_data })

(Which is what I assume you want anyways)

answered Apr 21, 2018 at 10:48

Joost

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1 Comment

MarkoShiva Over a year ago

sorry how that slipped out thanks i forgot to append the dicitionary instead of the return array.

metmirr · Accepted Answer · 2018-04-21 10:59:15Z

1

The problem is:

output = []

for user in users:
  ...
  output.append({'extensions' : output})  # here you are adding output to the output

check this example:

out = []
for i in range(2):
    out.append({'ext': out})
# output
[{'ext': [...]}, {'ext': [...]}]

You have the same output. I am sure this is not what you want. So change the line with problem to this one: output.append({'extensions' : user_data})

edited Apr 21, 2018 at 10:59

answered Apr 21, 2018 at 10:47

metmirr

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