compute model field by related field

[omar ahmed]

hello ... i have two models "Club" class and "Match" class and it has foreign key to Club

now i want to increment "won" field (or draw or lost) in "Club" class by "score_local" and "score_visitor" in "Match" class ..

how can i do this

class Club(models.Model):

name = models.CharField(max_length=100)

won = models.IntegerField(default=1)

draw = models.IntegerField(default=1)

lost = models.IntegerField()

goal_for = models.IntegerField()

goal_against = models.IntegerField()

class Match(models.Model):

play_date = models.DateTimeField('play date')

club_visitor = models.ForeignKey(Club, on_delete=models.CASCADE, related_name='match_club_visitor')

club_local = models.ForeignKey(Club, on_delete=models.CASCADE, related_name='match_club_local')

score_visitor = models.IntegerField()

score_local = models.IntegerField()

[Makori Breens]

Implement rest framework

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[Derek]

1. Add a "winner" field to your Match

2. Implement a post_save  signal for the Match model that updates the "won" or "lost" fields for each Club in the match (simple if/then logic based on winner).

PS I think the default values for "won" and "lost" for a Club should be "0" and not "1".

[omar ahmed]

thank you for response , derek
but how can i increment 'win' 'lost' or 'draw' Club fields by 'winner' Match field

[Derek]

That should just require a basic if/then logic test; "get" the correct Club object, update the win/loss field and save the Club. Repeat for both Clubs.

[omar ahmed]

i put this function in "Match" class :

def points(self):

if self.score_local > self.score_visitor:

return (self.club_local.won)+1 and (self.club_visitor.lost)+1

elif self.score_local < self.score_visitor:

return (self.club_local.lost)+1 and (self.club_visitor.won)+1

else:

return (self.club_local.draw)+1 and (self.club_visitor.draw)+1

and i want it to update fields and 'CalcPoints' function in "Club" class

class Club(models.Model):

...

def CalcPoints(self):

return self.won*3 + self.draw

but until now it does not update objects (( how can i use post_save here ))

[Derek]

You need to use Django signals to provide a custom "post_save".  There is a good tutorial here:
https://simpleisbetterthancomplex.com/tutorial/2016/07/28/how-to-create-django-signals.html

[omar ahmed]

yes i studied this tutorial before and i added this function to "Club" class (( Receiver function class )) but it does not affect fields

def teampoints( sender, instance, **kwargs):

if instance.score_local > instance.score_visitor:

return instance.club_local.won +1 and instance.club_visitor.lost + 1

elif instance.score_local < instance.score_visitor:

return instance.club_local.lost + 1 and instance.club_visitor.won + 1

else:

return instance.club_local.draw + 1 and instance.club_visitor.draw + 1

[Derek]

Did you add the required decorator before this function?  (The function is not part of the class; its a standalone appearing in the same module.)

Also, you generally don't put returns in the post_save function: but you do need to call save() on the model instance.

Another example here:
https://stackoverflow.com/questions/13014411/django-post-save-signal-implementation

[omar ahmed]

ok Derek i used save() instead of return and it works now
thank you very much

@receiver(post_save, sender=Match)

def update_club_score(instance, sender, **kwargs):

# club local won

if instance.score_local > instance.score_visitor:

instance.club_local.won += 1

instance.club_local.save()

instance.club_visitor.lost += 1

instance.club_visitor.save()

# club local lost

if instance.score_local < instance.score_visitor:

instance.club_local.lost += 1

instance.club_local.save()

instance.club_visitor.won += 1

instance.club_visitor.save()

# draw

if instance.score_local == instance.score_visitor:

instance.club_local.draw += 1

instance.club_local.save()

instance.club_visitor.draw += 1

instance.club_visitor.save()