Hi. select_related is used for folloing foreign keys. So if u have, say,
product and its producer field in it u can do smth like:
Product.objects.select_related('producer') and in ur templates accessing
product.producer won't hit the database.
Notice that here we have a relationship where only one producer can be
ralated to product. But you obviously can't do it when you have multiple
objects attached to one.
What you really need is
prefetch_related<https://docs.djangoproject.com/en/1.7/ref/models/querysets/#prefetch-related>
:
Producer.objects.prefetch_related('review_set', 'comments_set') will
populate product.review_set.all() and product.comments_set.all() for you.
четверг, 1 мая 2014 г., 17:22:52 UTC+4 пользователь Andreas Bloch написал:
>
> Okay, I'm a little confused here about using select_ralated...
>
> Can you only run select_related on a table that HAS a foreign key not a
> table that IS a foreign key?
>
> What if I want to go:
> SELECT * FROM product LEFT JOIN review on product.id = review.product_id
> LEFT JOIN comments ON product.id = comment.product_id
>
> example models.py
>
> class Product(models.Model):
> name =
>
> class Review(models.Model):
> product = models.Foreignkey(Product)
> rating =
>
> class Comments(models.Model):
> product = models.Foreignkey(Product)
> text =
>
> In my templates I want to be able to loop through all reviews and comments
> for each product without hitting the database multiple times...
>
> How can you achieve this?
>
>
>
>
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