Create objects from one model based on new object in another model (Django)

Question

Fairly new to Django (1.2), but just testing stuff out.

My headache is figuring out a way to create a series of SKU objects when a Product object is created.

class Product(models.Model):
    name = models.CharField(max_length=255, unique=True)
    style = models.CharField(max_length=50)
    colors = models.ManyToManyField(Color)
    sizes = models.ManyToManyField(Size)

class SKU(models.Model):
    id = models.CharField(max_length=15, unique=True, primary_key=True)
    style = models.ForeignKey(Product)
    color = models.ForeignKey(Color)
    size = models.ForeignKey(Size)
    quantity = models.IntegerField(default=0)

I initially tried to handle this in Product.save, but alas, no dice. I then tried this signals setup:

# models.py
def create_skus(sender, instance, *args, **kwargs):
    if 'created' in kwargs:
        if kwargs['created']:
            for x in instance.colors.select_related():
                for y in instance.sizes.select_related():
                    sku = instance.style
                    sku += instance.x.shortcode
                    sku += instance.y.name
                    s = SKU(id=sku, style=instance, color=x, size=y)
                    s.save()

... # after the Product class
post_save.connect(create_skus, sender=Product)

Some examples I've seen call for the sender class save method to have something like this:

def save(self):
    post_save.send(create_skus, self)

...and that's where I'm at. This setup doesn't throw any errors, but it also doesn't create said SKUs.

If I'm way off on any of this signals-wise, any pointers would be appreciated. Or if there's another technique to accomplish a similar feat, that would be wonderful as well.

Cheers!

Did you set debug markers? Ensure that your method gets into the loops (and please avoid "x" and "y", but take" "color" and "size") to find out what happens here. The way you implement the signal looks good for me. — schneck, Feb 21 '11 at 11:16

score 1 · Accepted Answer · answered Feb 21 '11 at 11:28

def create_skus(sender, instance, *args, **kwargs):
        if kwargs['created']:
            for color in instance.colors.select_related():
                for size in instance.sizes.select_related():
                    sku = u'%s%s%s' % (instance.style, color.shortcode, size.name) 
                    s = SKU(id=sku, style=instance, color=color, size=size)
                    s.save()

post_save.connect(create_skus, sender=Product)

This should work? If not, try installing the Debug Toolbar and checking that select_related() is returning the results you are expecting.

Create objects from one model based on new object in another model (Django)

1 Answers1