Return database information using json in Flask

Question

I can't figure out how to return the information from my database when using GET method because I keep getting errors in my return statements. I keep getting errors like object not subscriptable or stuff to do with dicts.

I tried.

return jsonify({'developers': User.query.all()})

I got the error TypeError: <main.User object at 0x038FC9D0> is not JSON serializable

When i try

return json.dumps(tuple[User.query.all()])

I get the error. TypeError: 'type' object is not subscriptable

from flask import Flask, jsonify,json
from flask_sqlalchemy import SQLAlchemy


app = Flask(__name__)
app.config.from_pyfile('Config.py')
db = SQLAlchemy(app)

class User(db.Model):
    User_ID = db.Column(db.Integer, primary_key = True)
    firstName = db.Column(db.String(20))
    lastName = db.Column(db.String(20))


   def __init__(self,firstName, lastName):
       self.firstName = firstName
       self.lastName = lastName
       db.create_all()

@app.route('/', methods = ['GET'])
def index():
    return json.dumps(tuple[User.query.all()])

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

type object is not subscriptable when i use json.dumps. I tried return jsonify as well but it get the eror that the object is not JSON serializable — new programmmmmer
– new programmmmmer, Commented Nov 2, 2016 at 5:04
Edit your question and include the tracebacks of the error(s). — Rushy Panchal
– Rushy Panchal, Commented Nov 2, 2016 at 5:04
Do you mean tuple(User.query.all())? Use of (...) instead of [...] for type-casting to tuple. Also provide the complete stack-trace — Moinuddin Quadri
– Moinuddin Quadri, Commented Nov 2, 2016 at 5:07
umm when i try tuple it says too many values to unpack and it expects 3. the table has 3 columns with like 10 rows — new programmmmmer
– new programmmmmer, Commented Nov 2, 2016 at 5:11

sberry · Accepted Answer · 2016-11-02 05:30:23Z

1

There are a couple problems. For one, SQLAlchemy db.Model types are not json serializable. That fact is covered up when you try to use tuple[...] as another error, but even if you fix that to tuple(...) you will get back to the original issue.

This should work, using a mixin that will json serialize for you. I think this will still have issues with datetime objects, but you can modify the as_dict method to handle that.

class JsonModel(object):
    def as_dict(self):
       return {c.name: getattr(self, c.name) for c in self.__table__.columns}

class User(db.Model, JsonModel):
    User_ID = db.Column(db.Integer, primary_key = True)
    firstName = db.Column(db.String(20))
    lastName = db.Column(db.String(20))


    def __init__(self,firstName, lastName):
       self.firstName = firstName
       self.lastName = lastName
       db.create_all()

@app.route('/', methods = ['GET'])
def index():
    return json.dumps([u.as_dict() for u in User.query.all()])

Tips:

Turning on app.debug = True while developing is also a good idea.
Running db.create_all in your init may be a bad idea.
Using jsonify is nice because it handles the Content-Type header as well.

> kurl -i http://localhost:5000
HTTP/1.0 200 OK
Content-Type: application/json
Content-Length: 102
Server: Werkzeug/0.8.3 Python/2.7.10
Date: Wed, 02 Nov 2016 05:28:42 GMT

{
  "users": [
    {
      "lastName": "Berry",
      "User_ID": 1,
      "firstName": "Sean"
    }
  ]
}

edited Nov 2, 2016 at 5:30

answered Nov 2, 2016 at 5:25

sberry

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1 Comment

new programmmmmer Over a year ago

Thanks! Been stuck on this for a long time.

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