How to add data to a ManyToMany field model?-CodePudding

I have model Department:

class Department(models.Model):
    id = models.AutoField(primary_key=True)
    title = models.CharField(max_length=30)
    subsidiary = models.ManyToManyField('self',null=True,blank=True, symmetrical=False, related_name='subsidiary_name')
    superior = models.ForeignKey('self',null=True,blank=True, related_name='superior_name', on_delete = models.DO_NOTHING)
    manager = models.ForeignKey(Manager, on_delete = models.DO_NOTHING)
    history = HistoricalRecords()

def get_subsidiary(self):
        return "\n".join([p.title for p in self.subsidiary.all()])

def __str__(self):
    return self.title

In Department model I have 2 instance of the same model: subsidiary and superior departments. The rules are simple: one department can have only one superior department, and many subsidiary. I want to implement next logic:

I am creating new department SLF, and f.e. I choose SID department as superior department for SLF. Finally, when I save SLF object I want to add this department as subsidiary for SID automatically.

I am trying to override save method like:

def save(self, *args, **kwargs):
    print('Department.objects.filter(title=self.superior): ', Department.objects.filter(title=self.superior))
    if self.superior__in == Department.objects.filter(title=self.superior.title):
        tmp = Department.objects.filter(title=self.superior.title)
        tmp.create(subsidiary = self.superior)
        tmp.save()

    super(Department, self).save(*args, **kwargs)

But it doesn't work. How can implement something like this?

CodePudding user response：

You have to use add() function to add new object to ManyToManyField. Remember also, that with filter you get QuerySet. To get object you should ust get or even get_object_or_404, but look yourself for that :)

...
    tmp = Department.objects.get(title=self.superior.title)
    tmp.subsidiary.add(self.superior)
...

You don't need to save it.

CodePudding user response：

Finally,

def save(self, *args, **kwargs):
        super(Department, self).save(*args, **kwargs)
        if self.superior == Department.objects.get(title=self.superior.title):
            tmp = Department.objects.get(title=self.superior.title)
            tmp.subsidiary.add(self)

Thank you for your advices.