GQL Query in AppEngine

Question

Im working with the dataStore trying to perfom a simple query, but it doesnt work as supposed to:

class User_Machine(db.Model):
    machine_id = db.IntegerProperty (required = True)
    username = db.StringProperty (required = True)
    last_call = db.DateTimeProperty (auto_now = True)

def query(username, machine_id)
    q = db.GqlQuery('SELECT * FROM User_Machine WHERE username=:1 AND machine_id=:2', username, machine_id)
    r = q.get()
    return r

print query('uherran', 23)

And my response is:

None

And I was expecting to read this record:

The values in the datastopre viewer are:

Enitty Kind  User_Machine
Entity Key   ahBkZXZ-Z2VzdG9yYXZpc29zchILEgxVc2VyX01hY2hpbmUYKAw
ID   40
username (string)   uherran
last_call (datetime)    2012-08-19 09:57:35
machine_id (long)       23

There must be something completely wrong in my understanding on how querys go.

Anyone can help?

Thanks.

In fact. I adapted a little but my code to provide clarity, but it seems I didnt make a propper error check.

The code is:

def check_machine_username(self, machine_id, username):
        key='CHECK_MACHINE_USERNAME_'+machine_id+'_'+username
        q= memcache.get(key)
        if q:
            return True
        else:
            logging.info(username)
            logging.info(machine_id)
            q = dbstructure.User_Machine.all()
            q.filter('username = ', username)
            q.filter('machine_id = ', machine_id)

            if q.get():
                loggin.info('query right')
                memcache.set(key,True)
                return True
            else:
                logging.info('query wrong')
                return False

No matter what I have in my User_machine db that query always returns empty.

Answer 1

My guess is that in the failing case your machine_id is a string, whereas it should be an int.

Answer 2

The problem as I notice it, was that machine_id was an integer and I was using a string.

q.filter('username = ', username)
q.filter('machine_id = ', int(machine_id))
                          ^^^

Its the bad thing about asuming a type.

Thanks to every one.

Answer 3

It looks like it is because you aren't returning the value of the function back to your print (I may or may not do this all the time as well :) ). Try this:

def query(username, machine_id)
    q = db.GqlQuery('SELECT * FROM User_Machine WHERE username=:1 AND machine_id=:2', username, machine_id)
    r = q.get()
    return r # or just return q.get()

Note that this will return a User_Machine object (and not a formatted dictionary/other response like you may be expecting) which you'll then need to handle (e.g. instead of print, assign it to a result variable and then you can access its attributes by doing result.machine_id, etc.).

You can also use a Query object to accomplish the same thing:

def query(username, machine_id)
    # Same as using SELECT * in the Gql query above)
    q = User_Machine.all()

    # Then apply the filters (you can also do q.filter(..).filter(..))
    q.filter('username = ', username)
    q.filter('machine_id = ', machine_id)
    return q.get()