CODEWITHSUNDEEP
pythondjangopython-3.xpython-2.7django-models
PeeKay
PeeKay

Reputation: 167

How to join two tables in Django ORM without any column in first table referencing the second

Check the models below

Now I want to join the tables and get product name and price

I cannot join the tables as I have no column in Product model referencing Price model

class Product(models.Model):
    name = models.CharField(max_length=100)

class Price(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    price = models.IntegerField()

Upvotes: 2

Views: 118

Answers (1)

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 476813

You can use .select_related(...) on the Price model, like:

prices = Price.objects.select_related('product')

Then you can for example iterate over it, and print the product name together with the price, like:

for price in prices:
    print('{}: {}'.format(price.product.name, price.price))

or you can use .annotate(...) to take fields from a related model, like:

from django.db.models import F

products = Product.objects.annotate(price=F('price__price'))

and then print it with:

for product in products:
    print('{}: {}'.format(product.name, product.price))

Finally you can .prefetch_related(...) the Prices, and then iterate over these, like:

products = Product.objects.prefetch_related('price_set')

for product in products:
    prices = product.price_set.all()
    if prices:
        for price in prices:
            print('{}: {}'.format(product.name, price.price))
    else:
        print('No prices for {}'.format(product.name))

That being said, if the price does not change in time, by country, etc. then it might be better to store the price in the Product.

Upvotes: 1

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