Random match-up with Python and Google App Engine

Question

I am building a website where two music videos are randomly chosen from a database and go head-to-head for voting. I need an algorithm that will continue picking unique match-ups for a user excluding match-ups they have had in the past, but with replacing videos for new match-ups. You can view a sample of the page here: http://10.showtownmvp.appspot.com/

I am running this on Google App Engine - Python, and have a voting table and videos table that stores the results. I would like to keep it as random as possible and avoid multiple queries, so if you have suggestions on how to model this in NDB or have a good algorithm, I would appreciate your help!

You can't just request random entity from the datastore. How much videos do you have? For really small datasets you can fetch all keys and then just do `random.choice(keys)`. — Dmytro Sadovnychyi, Mar 29 '14 at 06:31

score 1 · Answer 1 · answered Apr 02 '14 at 14:23

My solution to this problem was to query all videos from the datastore and randomly select one. I also ran a query for past votes / matchups for the user and converted this to a list so I could manipulate it without running several queries. Using the random video, I used a while loop to find a second video that was not in the previous matchup list. If no video was found, the program would remove the random choice from the video list, then select a new sample and run the search again. The code is below:

    class MainHandler(views.Template):              

        def post(self):
            # NOTE: we are posting genre and state.
            user = self.user_check()
            self.videos = models.videos.Videos.fetch_featured()

            try:
                random.sample(self.videos,2)

                if user:
                    self.user_votes = models.voting.Voting.query_by_user(user.key)

                    if self.user_votes != None:
                        self.user_votes = [[x.video_one,x.video_two] for x in self.user_votes]
                        page_vids = False
                        while page_vids == False and len(self.videos)>1:
                            rand_vid = random.choice(self.videos)
                            page_vids = self.find_match(rand_vid)
                            self.videos.remove(rand_vid)
                    else:
                        page_vids = random.sample(self.videos,2)

                else:
                    page_vids = random.sample(self.videos,2)

            except:
                page_vids = None


        def find_match(self, rand_vid):
            i =0

            while i < len(self.videos):
                if rand_vid.key != self.videos[i].key and ([rand_vid.key,self.videos[i].key] not in self.user_votes and [self.videos[i].key, rand_vid.key] not in self.user_votes):
                    return [rand_vid,self.videos[i]]
                i+=1
            return False




    class Videos(ndb.Model):
        acc_key = ndb.KeyProperty()
        musician_key = ndb.KeyProperty()
        musician_name = ndb.StringProperty()
        embed_link = ndb.StringProperty()
        genre_tag = ndb.StringProperty()
        video_title = ndb.StringProperty()
        featured = ndb.BooleanProperty(default = False)
        likes_count = ndb.IntegerProperty()
        video_added = ndb.DateTimeProperty(auto_now_add = True)

        @classmethod
        def query_by_account(cls, acc_key):
            return cls.query(cls.acc_key == acc_key).fetch()

        @classmethod
        def fetch_featured(cls):
            return cls.query(cls.featured == True).fetch(100)


class Voting(ndb.Model):
        voter_acc_key = ndb.KeyProperty()
        voter_type = ndb.StringProperty()
        video_one = ndb.KeyProperty()
        video_one_artist_key = ndb.KeyProperty()
        video_two = ndb.KeyProperty()
        video_two_artist_key = ndb.KeyProperty()
        voter_choice = ndb.KeyProperty()
        video_set_check = ndb.KeyProperty(repeated = True)
        voter_ip = ndb.StringProperty()
        vote_time = ndb.DateTimeProperty(auto_now_add = True)


        @classmethod
        def query_by_user(cls, acc_key):
            return cls.query(cls.voter_acc_key == acc_key).fetch(2000)

Random match-up with Python and Google App Engine

1 Answers1