Django: make a list of column elements of selected rows-CodePudding

I'm new on Django and SQL and I'm trying to solve some simple problems to start to understand them.

I have 3 models: Client, Product and Order. I want to list the products ordered by a client.

The models:

class Client(models.Model):
    name = models.CharField(max_length=32)
    .....

class Product(models.Model):
    product_name = models.CharField(max_length=32)
    .....

class Order(models.Model):
    client = models.ForeignKey(Client,on_delete=models.CASCADE)
    product = models.ForeignKey(Product,on_delete=models.CASCADE)
    .....

My solution was:

client= Client.objects.get(id=1) # target client
orders = client.order_set.all()
# or alternatively orders = Order.objects.filter(client=client)
list_of_orders=[order.product for order in orders]

My question: is there a better solution that uses some features of Django to get the list, instead of the for loop?

CodePudding user response：

In your case, you can select only products from the queryset using values_list(), you can add the values which you want to return for example:

products = Order.objects.filter(client=client).values_list('product__product_name', flat=True)

the example apove will return a list of product names.

You can read how it works here values_list in Django

CodePudding user response：

From a deeper search in the Django documentation, I found that the for loop is actually used to solve the case of my question.

To avoid a db query each loop iteration, Django provides the methods select_related() and prefetch_related().

Please see the two methods in this page