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POHow can I have model field names (or operators) in a variable?
 

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  1. POHow can I have model field names (or operators) in a variable?
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    <p>I'm trying to refactor my little voting functions. I've got two of them which do almost exactly the same thing, only to different model fields. Voters can add stars to a song if they like it, and they can add flags to a song if they dislike it. The voters are then associated with the song via a many2many relationship, so it can be determined if they already voted on that song. If so, a star (or a flag) is removed from the song and the relationship between voter and song is removed also.</p> <p>Here is the function that adds or removes stars:</p> <pre><code># models.py class UserProfile(models.Model): user = models.ForeignKey(User, unique = True, related_name = 'profile') liked_songs = models.ManyToManyField('Song', blank = True, null = True) disliked_songs = models.ManyToManyField('Song', blank = True, null = True) class Song(models.Model): song_id = models.CharField(max_length = 36, primary_key = True) last_accessed = models.DateTimeField() stars = models.IntegerField(max_length = 5, default = 0) flags = models.IntegerField(max_length = 5, default = 0) # views.py def vote(request, song_id, task): # 'task' should be either 'stars' or 'flags' song = Song.objects.get(song_id = song_id) voter = request.user.get_profile() # Voter does not already like the song if not voter.liked_songs.filter(song_id = song.song_id): # (*) try: # Increase vote, set 'last_accessed', add Song to UserProfile.liked_songs Song.objects.filter(song_id = song_id).update( stars = F('stars') + 1, # (*) last_accessed = datetime.datetime.now() ) voter.liked_songs.add(song) # (*) except: raise else: try: # Decrease vote, set 'last_accessed', remove Song from UserProfile.liked_songs Song.objects.filter(song_id = song_id).update( stars = F('stars') - 1, # (*) last_accessed = datetime.datetime.now() ) voter.liked_songs.remove(song) # (*) except: raise return "Done." </code></pre> <p>The function that adds or removes flags is exactly the same, except for the marked (*) lines:</p> <pre><code>if not voter.disliked_songs.filter(song_id = song.song_id) flags = F('flags') + 1, flags = F('flags') - 1, voter.disliked_songs.add(song) voter.disliked_songs.remove(song) </code></pre> <p>Now here's my first question: What do I have to do to use only one function for liking and disliking a song? I have already introduced the argument <code>task</code> but I can't seem to write <code>task = F('task') + 1,</code>, because there is no field name 'task' in the Song model.</p> <p>Bonus question: The only difference between <code>stars = F('stars') + 1,</code> and <code>stars = F('stars') - 1,</code> is the operator (<code>+</code> or <code>-</code>). Is there a way to have an operator in a variable, i.e. <code>task = F('task') myoperator 1,</code>?</p>
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