I am currently developing an application with Flask-Restless. When I substituted my SQLAlchemy models' typical DateTime fields with corresponding arrow fields, all went smoothly. This was due to the help of SQLAlchemy-Utils and its ArrowType field.
However, after using the API to return a JSON representation of these objects, I received the following error:
TypeError: Arrow [2015-01-05T01:17:48.074707] is not JSON serializable
Where would be the ideal place to modify how the model gets serialized? Do I modify Flask-Restless code to support Arrow objects or write a model method that Flask-Restless can identify and use to retrieve a JSON-compatible object?
I could also write an ugly post-processor function in the meantime but that solution seems like a terrible hack.
Below is an example model with the ArrowType field:
id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.Unicode, unique=True, nullable=False)
created_at = db.Column(ArrowType, nullable=False)
def __init__(self, title):
self.title = title
self.created_at = arrow.utcnow()
How about a custom
JSONEncoder which supports Arrow types? Looking at the Flask-Restless source code, it uses Flask's built in
jsonify under the hood. See this snippet for an example which serializes regular
datetime objects in a different format: http://flask.pocoo.org/snippets/119/
Here's a full self-contained example for good measure:
import flask import flask.ext.sqlalchemy import flask.ext.restless from flask.json import JSONEncoder import sqlalchemy_utils import arrow app = flask.Flask(__name__) app.config['DEBUG'] = True app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db' db = flask.ext.sqlalchemy.SQLAlchemy(app) class Event(db.Model): id = db.Column(db.Integer, primary_key=True) timestamp = db.Column(sqlalchemy_utils.ArrowType) class ArrowJSONEncoder(JSONEncoder): def default(self, obj): try: if isinstance(obj, arrow.Arrow): return obj.format('YYYY-MM-DD HH:mm:ss ZZ') iterable = iter(obj) except TypeError: pass else: return list(iterable) return JSONEncoder.default(self, obj) app.json_encoder = ArrowJSONEncoder db.create_all() manager = flask.ext.restless.APIManager(app, flask_sqlalchemy_db=db) manager.create_api(Event, methods=['GET','POST']) app.run()
From the two options in your post, I'd suggest adding the method to your model class to retrieve a JSON-compatible object, only because it's simpler and more maintainable. If you want to modify Flask-Restless, you either need to fork it or monkey patch it.