from google.appengine.ext import ndb

# Datastore Model for a Student.
class Student(ndb.Model):
    first_name = ndb.StringProperty()
    last_name = ndb.StringProperty()
    credits = ndb.IntegerProperty()

# Datastore Model for a Wand that stores a reference to its owner.
class Wand(ndb.Model):
    core = ndb.StringProperty()
    wood_type = ndb.StringProperty()
    model = ndb.IntegerProperty()
    length = ndb.FloatProperty()
    # 'owner' is a reference to a Student via a Key.
    owner = ndb.KeyProperty(kind="Student")

class House(ndb.Model):
    name = ndb.StringProperty()
    points = ndb.IntegerProperty()
    members = ndb.KeyProperty(kind=Student, repeated=True)

# If gryffindor doesn't exist, make new instance and add to datastore
# gryffindor = House(name="Gryffindor", points=500, members=[])
# gryffindor.put()

gryffindor = House.query(House.name == "Gryffindor").get()

# Create new student and add to Gryffindor
ron = Student(first_name="Ron", last_name="Weasley")
ron_key = ron.put()

gryffindor.members.append(ron_key)
gryffindor.put() # remember to commit to the datastore so it sees your change!