Django：使用信号保存ManyToMany字段 [英] Django: Using signals to save a ManyToMany field

问题描述

我正在尝试将一个ManyToMany字段保存在模型中。由于对象不存在，所以在save（）方法中不可能这样做。所以我试着把逻辑放在一个信号中。我的问题是：每当我创建一个新的FaculteAdmissions对象时，信号似乎都会发射两次。主要症状是信号输出复制。这是代码，这将会更明显。

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.

型号：

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"

关联信号：

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))

和信号连接：

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

推荐答案

正如@karthikr所说，正确的使用信号是 m2m_changed 。

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

只需从 post_save 切换到该信号即可。

Simply switching to that signal from post_save did the trick.

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