Google app engine database values not incrementing

Question

Here is some code that is not working how it is supposed to work. Every time the database is queried, I get either a 0 or 1 value for the options, and the values in database do not increment, even though as as you can see, in line 86 and 89, the values are being incremented. Any idea what's going wrong here? I am using Django on Google App engine.

        user_result = request.POST['json']
 65     user_result = json.loads(user_result)
 66     user_country = get_user_country(user_result)
 67     question_number = get_question_number(user_result)
 68     answered_option = get_answered_option(user_result)
 69 
 70     country_option_1 = 0
 71     country_option_2 = 0
 72     world_option_1 = 0
 73     world_option_2 = 0
 74 
 75     """
 76     Get already existing record for the question for the contry, or create
 77     new one and put/update in db
 78     """
 79 
 80     country_wide_data = db.GqlQuery("SELECT * FROM CountryWideData WHERE country = :1 AND questionNo = :2", user_country, question_number)
 81     flag = False
 82     for i in country_wide_data:
 83         flag = True
 84     if flag:
 85         if answered_option==1:
 86             country_wide_data[0].optionOne = country_wide_data[0].optionOne + 1
 87 
 88         elif answered_option==2:
 89             country_wide_data[0].optionTwo = country_wide_data[0].optionTwo + 1
 90         country_option_1 = country_wide_data[0].optionOne
 91         country_option_2 = country_wide_data[0].optionTwo
 92         country_wide_data[0].put()
 93     else:
 94         country_wide_data = CountryWideData(country=user_country, questionNo=question_number)
 95 
 96         if answered_option==1:
 97             country_wide_data.optionOne = 1
 98             country_wide_data.optionTwo = 0
 99         elif answered_option==2:
100             country_wide_data.optionOne = 0
101             country_wide_data.optionTwo = 1
102         country_option_1 = country_wide_data.optionOne
103         country_option_2 = country_wide_data.optionTwo
104         country_wide_data.put()

Answer 1

You are never using fetch() to actually execute the GqlQuery that you create in line 80.

Try this:

country_wide_data = db.GqlQuery("SELECT * FROM CountryWideData WHERE country = :1 AND questionNo = :2", user_country, question_number).fetch()

By the way, you are going to want to do this incrementing inside of a transaction; otherwise, you will get a race condition if more than one request can execute this code, and the counts will be inaccurate. The documentation on transactions is here: http://code.google.com/appengine/docs/python/datastore/transactions.html

Generally, you are going to want to take the code that creates or updates these entities and put them into functions, like this:

def increment_existing_data(key, answered):
    cwd_to_incr = db.get(key)
    if answered == 1:
        cwd_to_incr.optionOne += 1
    elif answered == 2:
        cwd_to_incr.optionTwo += 1
    cwd_to_incr.put()

def create_new_data(answered, user_country, question_number):
    new_data = CountryWideData(country=user_country, questionNo=question_number)
    if answered == 1:
        new_data.optionOne = 1
        new_data.optionTwo = 0
    elif answered == 2:
        new_data.optionOne = 0
        new_data.optionTwo = 1
    new_data.put()

Then, you can call these functions using the db.run_in_transacation method, like this:

country_wide_data = db.GqlQuery("SELECT * FROM CountryWideData WHERE country = :1 AND questionNo = :2", user_country, question_number).get()
if country_wide_data is not None:
    db.run_in_transaction(increment_existing_data, country_wide_data.key(), answered_option)
else:
    db.run_in_transaction(create_new_data, answered_option,  user_country, question_number)