Google App Engine Datastore Query to JSON with Python

How can I get a JSON Object in python from getting data via Google App Engin开发者_开发知识库e Datastore?

I've got model in datastore with following field:

id
key_name
object
userid
created

Now I want to get all objects for one user:

query = Model.all().filter('userid', user.user_id())

How can I create a JSON object from the query so that I can write it?

I want to get the data via AJAX call.

Not sure if you got the answer you were looking for, but did you mean how to parse the model (entry) data in the Query object directly into a JSON object? (At least that's what I've been searching for).

I wrote this to parse the entries from Query object into a list of JSON objects:

def gql_json_parser(query_obj):
    result = []
    for entry in query_obj:
        result.append(dict([(p, unicode(getattr(entry, p))) for p in entry.properties()]))
    return result

You can have your app respond to AJAX requests by encoding it with simplejson e.g.:

query_data = MyModel.all()
json_query_data = gql_json_parser(query_data)
self.response.headers['Content-Type'] = 'application/json'
self.response.out.write(simplejson.dumps(json_query_data))

Your app will return something like this:

[{'property1': 'value1', 'property2': 'value2'}, ...]

Let me know if this helps!

If I understood you correctly I have implemented a system that works something like this. It sounds like you want to store an arbitrary JSON object in a GAE datastore model. To do this you need to encode the JSON into a string of some sort on the way into the database and decode it from a string into a python datastructure on the way out. You will need to use a JSON coder/decoder to do this. I think the GAE infrastructure includes one. For example you could use a "wrapper class" to handle the encoding/decoding. Something along these lines...

class InnerClass(db.Model):
    jsonText = db.TextProperty()
    def parse(self):
        return OuterClass(self)

class Wrapper:
    def __init__(self, storage=None):
        self.storage = storage
        self.json = None
        if storage is not None:
            self.json = fromJsonString(storage.jsonText)
    def put(self):
        jsonText  = ToJsonString(self.json)
        if self.storage is None:
            self.storage = InnerClass()
        self.storage.jsonText = jsonText
        self.storage.put()

Then always operate on parsed wrapper objects instead of the inner class

def getall():
    all = db.GqlQuery("SELECT * FROM InnerClass")
    for x in all:
        yield x.parse()

(untested). See datastoreview.py for some model implementations that work like this.

I did the following to convert the google query object to json. I used the logic in jql_json_parser above as well except for the part where everything is converted to unicode. I want to preserve the data-types like integer, floats and null.

import json
class JSONEncoder(json.JSONEncoder):
    def default(self, obj):
        if hasattr(obj, 'isoformat'): #handles both date and datetime objects
            return obj.isoformat()
        else:
            return json.JSONEncoder.default(self, obj)

class BaseResource(webapp2.RequestHandler):
    def to_json(self, gql_object):
        result = []
        for item in gql_object:
            result.append(dict([(p, getattr(item, p)) for p in item.properties()]))
        return json.dumps(result, cls=JSONEncoder)

Now you can subclass BaseResource and call self.to_json on the gql_object