How to create a JSON file from a NDB database using Python - json

Question

I would like to generate a simple json file from an database.
I am not an expert in parsing json files using python nor NDB database engine nor GQL.
What is the right query to search the data? see https://developers.google.com/appengine/docs/python/ndb/queries
How should I write the code to generate the JSON using the same schema as the json described here below?
Many thanks for your help
Model Class definition using NDB:
# coding=UTF-8
from google.appengine.ext import ndb
import logging
class Albums(ndb.Model):
"""Models an individual Event entry with content and date."""
SingerName = ndb.StringProperty()
albumName = ndb.StringProperty()
Expected output:
{
"Madonna": ["Madonna Album", "Like a Virgin", "True Blue", "Like a Prayer"],
"Lady Gaga": ["The Fame", "Born This Way"],
"Bruce Dickinson": ["Iron Maiden", "Killers", "The Number of the Beast", "Piece of Mind"]
}

Answer 1

For consistency, model names should by singular (Album not Albums), and property names should be lowercase_with_underscores:
class Album(ndb.Model):
singer_name = ndb.StringProperty()
album_name = ndb.StringProperty()
To generate the JSON as described in your question:
1) Query the Album entities from the datastore:
albums = Album.query().fetch(100)
2) Iterate over them to form a python data structure:
albums_dict = {}
for album in albums:
if not album.singer_name in albums_dict:
albums_dict[album.singer_name] = []
albums_dict[album.singer_name].append(album.album_name)
3) use json.dumps() method to encode to JSON.
albums_json = json.dumps(albums_dict)
Alternatively, you could use the built in to_dict() method:
albums = Album.query().fetch(100)
albums_json = json.dumps([a.to_dict() for a in albums])