RESTful interface in Flask and issues serializing - json

Question

I'm learning Backbone.js and Flask (and Flask-sqlalchemy). I chose Flask because I read that it plays well with Backbone implementing RESTful interfaces. I'm currently following a course that uses (more or less) this model:
class Tasks(db.Model):
id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.String(80), unique=True)
completed = db.Column(db.Boolean, unique=False, default=False)
def __init__(self, title, completed):
self.title = title
self.completed = completed
def json_dump(self):
return dict(title=self.title, completed=self.completed)
def __repr__(self):
return '<Task %r>' % self.title
I had to add a json_dump method in order to send JSON to the browser. Otherwise, I would get errors like object is not JSON serializable, so my first question is:
Is there a better way to do serialization in Flask? It seems that some objects are serializable but others aren't, but in general, it's not as easy as I expected.
After a while, I ended up with the following views to take care of each type of request:
#app.route('/tasks')
def tasks():
tasks = Tasks.query.all()
serialized = json.dumps([c.json_dump() for c in tasks])
return serialized
#app.route('/tasks/<id>', methods=['GET'])
def get_task(id):
tasks = Tasks.query.get(int(id))
serialized = json.dumps(tasks.json_dump())
return serialized
#app.route('/tasks/<id>', methods=['PUT'])
def put_task(id):
task = Tasks.query.get(int(id))
task.title = request.json['title']
task.completed = request.json['completed']
db.session.add(task)
db.session.commit()
serialized = json.dumps(task.json_dump())
return serialized
#app.route('/tasks/<id>', methods=['DELETE'])
def delete_task(id):
task = Tasks.query.get(int(id))
db.session.delete(task)
db.session.commit()
serialized = json.dumps(task.json_dump())
return serialized
#app.route('/tasks', methods=['POST'])
def post_task():
task = Tasks(request.json['title'], request.json['completed'])
db.session.add(task)
db.session.commit()
serialized = json.dumps(task.json_dump())
return serialized
In my opinion, it seems a bit verbose. Again, what is the proper way to implement them? I have seen some extensions that offer RESTful interfaces in Flask but those look quite complex to me.
Thanks

Answer 1

I would use a module to do this, honestly. We've used Flask-Restless for some APIs, you might take a look at that:
https://flask-restless.readthedocs.org/en/latest/
However, if you want build your own, you can use SQLAlchemy's introspection to output your objects as key/value pairs.
http://docs.sqlalchemy.org/en/rel_0_7/core/schema.html#metadata-reflection
Something like this, although I always have to triple-check I got the syntax right, so take this as a guide more than working code.
#app.route('/tasks')
def tasks():
tasks = Tasks.query.all()
output = []
for task in tasks:
row = {}
for field in Tasks.__table__.c:
row[str(field)] = getattr(task, field, None)
output.append(row)
return jsonify(data=output)
I found this question which might help you more. I'm familiar with SQLAlchemy 0.7 and it looks like 0.8 added some nicer introspection techniques:
SQLAlchemy introspection

Answer 2

Flask provides jsonify function to do this. Check out its working here.
Your json_dump method is right though code can be made concise. See this code snippet
#app.route('/tasks')
def tasks():
tasks = Tasks.query.all()
return jsonify(data=[c.json_dump() for c in tasks])