Custom JSON encoder for Flask

gistfile1.txt

from flask import Flask
from flask import render_template
from flask import request
from flask import jsonify
import json


# This class tells Python how to turn a Delivery object into a JSON string. 
# This class could encode various types of objects - use isinstance to check what type of thing it is, and return the appropriate JSON
# https://docs.python.org/3/library/json.html

class DeliveryEncoder(json.JSONEncoder):
	def default(self, obj):
		
		if isinstance(obj, Delivery):
			return { 'to' : obj.to,  'from' : obj.fr }

		return json.JSONEncoder.default(self, obj) # default, if not Delivery object. Caller's problem if this is not serialziable.


app = Flask(__name__)

# Tell your app object which encoder to use to create JSON from objects. 
# TODO - what if there are different classes which will be encoded in different ways? 
# http://flask.pocoo.org/snippets/119/
app.json_encoder = DeliveryEncoder


# Example object to represent a model from the database
class Delivery:
	def __init__(self, to, fr):
		self.to = to
		self.fr = fr


# An example API call
@app.route('/api')
def get_json():

	d1 = Delivery('mpls', 'st paul')
	d2 = Delivery('roseville', 'mpls')

	# Pretend this list is the results of a database query
	l = [d1, d2]
 
	return jsonify( l )    # This turns the list of delivery objects into JSON
  
  '''
  Output looks like this
  
  [
  {
    "from": "st paul", 
    "to": "mpls"
  }, 
  {
    "from": "mpls", 
    "to": "roseville"
  }
]
  
  '''





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

return json.JSONEncoder.default(self, obj)

should be:

return super().default(self, obj)

Also one should not return JSON arrays in results but rather objects, because array results are attackable with XSS.

And in that case, per Flask documentation if you return a dict, it will encode it to JSON for you, so no need to use jsonify

# An example API call
@app.route('/api')
def get_json():
    d1 = Delivery('mpls', 'st paul')
    d2 = Delivery('roseville', 'mpls')
    # Pretend this list is the results of a database query
    return {
        'result': [d1, d2]
    } # This turns the dictionary with the list of delivery objects into JSON