CODEWITHSUNDEEP
pythondjango
slaughterize
slaughterize

Reputation: 734

Django: Using signals to save a ManyToMany field

I am trying to save a ManyToMany field post save in a model. It's not possible to do so in the save() method as the object does not exist. So I tried putting the logic in a signal instead. My problem is: the signal seems to fire twice everytime I create a new FaculteAdmissions object. The main symptom is that the signal output is duplicated. Here is the code, it'll be a bit more obvious.

Model:

class FaculteAdmissions(models.Model):
    trimestre = models.IntegerField(unique=True)
    session = models.CharField(max_length=25)
    annee = models.CharField(max_length=10)
    date_lecture = models.DateField()
    data = models.ManyToManyField(Admissions)

    def save(self, *args, **kwargs):
        """
        Exécuté avant la sauvegarde d'un objet de ce modèle.
        Validera si dans la table Admissions il existe des données pour ce trimestre.
        """
        # valide l'unicité
        if FaculteAdmissions.objects.filter(trimestre=self.trimestre).exists():
            raise ValidationError("Un objet ayant ces valeurs existe déjà")
        else:
            # valide les données
            q = Admissions.objects.filter(trimestre=self.trimestre,
                                          niveau=constantes.NIVEAUX_LECTURE_BD[2])
            if not q.exists():
                raise ValidationError("Données introuvables dans la table Admissions")

            # OK!
            super(FaculteAdmissions, self).save(*args, **kwargs)

            # Envoie signal pour mettre à jour les données
            post_save.send(sender=self.__class__, instance=self, created=True)

    def __str__(self):
        return "Faculté - Admissions"

associated signal:

def creation_faculte_admissions(sender, instance, created, **kwargs):
    if created:
        # valide les données
        q = Admissions.objects.filter(trimestre=instance.trimestre,
                                      niveau=constantes.NIVEAUX_LECTURE_BD[2])

        instance.data = q
        print("Données ajouté pour " + str(instance) + str(instance.trimestre))

and the signal connect:

post_save.connect(creation_faculte_admissions, sender=FaculteAdmissions, dispatch_uid="faculte_admissions")

Upvotes: 0

Views: 265

Answers (1)

slaughterize
slaughterize

Reputation: 734

As @karthikr mentionned, the correct signal to use is m2m_changed.

Simply switching to that signal from post_save did the trick.

Upvotes: 1

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