Keep track of objects created in the child model by updating the parent model-CodePudding

I have 2 models Parent, Child

class Parent(models.Model):
    description = models.CharField(max_length=250, null=True, blank=True)
    child_list = models.CharField(max_length=250, null=True, blank=True)

class Child(models.Model):
    price = models.CharField(max_length=250, null=False, blank=False)

I need to populate child_list whenever a Child object is created

I don't know if there is a predefined tool in Django for that, the goal is basically for each 'parent' to know how many children it has (with a list of the ids of its children).

What I had thought was to create a list with the ids of the children, but I think it is not efficient/elegant at all.

Does anyone know what would be the right way to do it?

CodePudding user response：

Like @dudulu said, you can use foreign keys for this.

Example:

class Faq(models.Model):
    name = models.CharField(max_length=255, default='none')
    email = models.CharField(max_length=255, default='none')
    subject = models.CharField(max_length=255, default='none')
    date = models.DateField(auto_now_add=True)

    def __str__(self):
        return self.subject

    def get_absolute_url(self):
        return reverse("faq_detail", kwargs={"pk": self.pk})

class Answers(models.Model):
    faqs = models.ForeignKey(
        "Faq", on_delete=models.CASCADE, null=True, related_name='answers')
    detail = models.TextField()
    date = models.DateField(auto_now_add=True, null=True)

Or something of the like.

This website on foreign keys helped me alot when I tried it myself.

CodePudding user response：

This should be what you want, this is the simplest example.

You should try to google django ForeignKey example.

First

class Parent(models.Model):
    description = models.CharField(max_length=250, null=True, blank=True)


class Child(models.Model):
    price = models.CharField(max_length=250, null=False, blank=False)
    parent = models.ForeignKey(Parent, on_delete=models.CASCADE)

First for

for p in Parent.objects.all():
    print(f'count: {p.child_set.count()}')
    for child in p.child_set.all():
        print(f'child: price: {child.price}')

Second

class Child(models.Model):
    price = models.CharField(max_length=250, null=False, blank=False)
    parent = models.ForeignKey(Parent, on_delete=models.CASCADE, related_name='custom_child')

Second for

for p in Parent.objects.all():
    print(f'count: {p.custom_child.count()}')
    for child in p.custom_child.all():
        print(f'child: price: {child.price}')

Simply take the ID List...

for p in Parent.objects.all():
    id_list = [child.id for child in p.custom_child.all()]