It is a Django project, I am trying to create a wishlist (many-to-many will not help because I need DateTime of getting that wished item in the wishlist).

class Client(models.Model):
    name = models.CharField(max_length=100)
    user = models.ForeignKey(User, on_delete=models.CASCADE)


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

class WishItem(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    client = models.ForeignKey(Client, related_name="wishlist", on_delete=models.CASCADE)
    added_at = models.DateTimeField(auto_now_add=True)

What I could do is only this:

wishlist = Client.objects.wishlist.select_related('product').all()
wish_products = [item.product for item in wishlist]

But I need something like this, without a loop but with a single SQL query and single line

wishlist = Client.objects.wishlist.product.all()

When I try to run this code I get an error AttributeError: 'RelatedManager' object has no attribute 'product'

CodePudding user response：

You can .filter(…) ^[Django-doc] and then .order_by(…) ^[Django-doc] with:

Product.objects.filter(wishitem__client__user=my_user).order_by('wishitem__added_at')

You can make it more covenient to query by spanning a ManyToManyField with your WishItem:

class Client(models.Model):
    # …
    wishlist = models.ManyToManyField(
        'Product',
        through='WishItem'
    )


class Product(models.Model):
    # …
    pass

class WishItem(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    client = models.ForeignKey(Client, related_name='wishitems', on_delete=models.CASCADE)
    added_at = models.DateTimeField(auto_now_add=True)

then you can query with:

Product.objects.filter(client__user=my_user).order_by('wishitem__added_at')

It will also make querying for the .wishlist of the Client more covenient, of the Products where the .client_set is a manager that manages the Clients that have that Product on the wishlist.

Note: It is normally better to make use of the settings.AUTH_USER_MODEL ^[Django-doc] to refer to the user model, than to use the User model ^[Django-doc] directly. For more information you can see the referencing the User model section of the documentation.

CodePudding user response：

Many to many relationship will fix the problem you can add extra fields to your WishItem class you can try this :

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

 class Client(models.Model):
    name = models.CharField(max_length=100)
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    WishProducts = models.ManyToManyField(Product,through='WishItem')


class WishItem(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    client = models.ForeignKey(Client, on_delete=models.CASCADE)
    added_at = models.DateTimeField(auto_now_add=True)