Get

keyname = firstmodel.key()
query = FirstModel.get(keyname)
print query

Count Instance method of Query Class

from google.appengine.ext import db
from google.appengine.api import users
 
class FirstModel(db.Model):
    prop = db.IntegerProperty()

class SecondModel(db.Model):
    prop2 = db.IntegerProperty()
    reference = db.ReferenceProperty(FirstModel, collection_name = "relation")



//Input data to datastore
firstmodel = FirstModel(prop = 06)
firstmodel.put()
secondmodel = SecondModel(prop2 = 1, reference = firstmodel)
secondmodel.put()
secondmodel = SecondModel(prop2 = 2, reference = firstmodel)
secondmodel.put()



//Count
query = firstmodel.relation
query_count = query.count()
print query_count

OR
query = FirstModel.all()
query_count = query.count()
print query_count

Result:
2

Google app engine simple query

from google.appengine.ext import db
from google.appengine.api import users

class FirstModel(db.Model):
prop = db.IntegerProperty()

class SecondModel(db.Model):
prop2 = db.IntegerProperty()
reference = db.ReferenceProperty(FirstModel, collection_name = "relation")


// Put data to datastore
firstmodel = FirstModel(prop = 06)
firstmodel.put()
secondmodel = SecondModel(prop2 = 1, reference = firstmodel)
secondmodel.put()
secondmodel = SecondModel(prop2 = 2, reference = firstmodel)
secondmodel.put()


Get all entity by using collection_name

query = firstmodel.relation
query = query.fetch(30)
print query



The Result
2 entity are displayed.
[<__main__.SecondModel object at 0x020736B0>, <__main__.SecondModel object at 0x02073790>]

TCAP