using data of queyset as input values of another model

Using Django Using the ORM
1

Hi every one
i have two models
one for saving product data

class Good(models.Model):
    mainbranch = models.ForeignKey(
        MainBranch, on_delete=models.CASCADE,
        verbose_name='کد دسته اصلی', default=0
    )
    subbranch1 = models.ForeignKey(
        SubBranch1, on_delete=models.CASCADE,
        verbose_name='کد دسته فرعی 1', default=0
    )
    subbranch2 = models.ForeignKey(
        SubBranch2, on_delete=models.CASCADE,
        verbose_name='کد کالا', default=0
    )
    subbranch3 = models.ForeignKey(
        SubBranch3, on_delete=models.CASCADE,
          verbose_name='نام کالا', default=0, related_name='good_name')
    goodproperties = models.OneToOneField(
        GoodProperties, on_delete=models.CASCADE,
        verbose_name='مشخصات کالا', null=True, blank=True
    )
    goodspecifications = models.OneToOneField(
        GoodSpecification, on_delete=models.CASCADE,
        verbose_name='معرفی کالا', default=0, null=True, blank=True
    )    
    image = models.ImageField(upload_to='photos/%Y/%m/%d', null=True, blank=True, verbose_name='تصویر کالا')
    quantity = models.PositiveIntegerField(default=0, verbose_name='تعداد موجود')
    price = models.DecimalField(
        decimal_places=0, max_digits=12, default=0,
        verbose_name='قیمت کالا'
    )
    discount = models.SmallIntegerField(null=True, blank=True, verbose_name='میزان تخفیف')
    seller = models.ManyToManyField('Seller', verbose_name='کد فروشنده')

and one for saving customers buy basket data

class BuyBasket(models.Model):
    customer = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, blank=True, null=True,
                                       verbose_name='کد مشتری')
    mainbranch = models.ForeignKey(
        MainBranch, on_delete=models.CASCADE, verbose_name='کد دسته اصلی کالا', default=0) # type: ignore
    subbranch1 = models.ForeignKey(
        SubBranch1, on_delete=models.CASCADE, verbose_name='کد دسته فرعی 1 کالا', default=0) # type: ignore
    subbranch2 = models.ForeignKey(
        SubBranch2, on_delete=models.CASCADE,verbose_name='کد دسته فرعی 2', default=0) # type: ignore
    subbranch3 = models.ForeignKey(
        SubBranch3, on_delete=models.CASCADE,verbose_name='نام کالا',default=0
    ) # type: ignore
    quantity = models.PositiveIntegerField(verbose_name='تعداد')
    price = models.ForeignKey(Good, on_delete=models.CASCADE, default=0, verbose_name='قیمت کالا') # type: ignore
    total_price = models.DecimalField(decimal_places=0, max_digits=16, default=0, verbose_name='مبلغ کل سفارش') # type: ignore
    change_to_order = models.BooleanField(blank=True, null=True, verbose_name='تبدیل به سفارش')

also this piece of code in my views.py that is going to add a product to customer’s basket

def add_to_buybasket(request, g_id):
    good_item = Good.objects.get(id=g_id) 
    if request.method == 'POST':
        form =QuantityForm(request.POST)
        if form.is_valid():
            value = form.cleaned_data['quantity']     
    obj, created = BuyBasket.objects.update_or_create(
        customer_id = request.user.id,
        mainbranch_id = good_item.mainbranch.id,
        subbranch1_id = good_item.subbranch1.id,
        subbranch2_id = good_item.subbranch2.id,
        subbranch3_id = good_item.subbranch3.id,        
        quantity = value,
        price_id = good_item.price, # here the problem appears
        total_price = value * good_item.price,
        change_to_order = False,
    )
    messages.success(request, 'کالا به سبد خرید شما اضافه شد')
    return HttpResponseRedirect(reverse('goods_list', kwargs={'pk': g_id}))

the problem is when i want to set price field of BuyBasket model with the value of corresponding Good one Django throws this error

insert or update on table "orders_buybasket" violates foreign key constraint "orders_buybasket_price_id_bbb4aff1_fk_goods_good_id"
DETAIL:  Key (price_id)=(18000000) is not present in table "goods_good".

Could you tell me where the problem is
Thanks

2

In model Good, you have:

But in model BuyBasket you have:

The price field is expecting to be assigned a reference to an instance of a Good object, not the result of a calculation. I expect that what you want is for this second occurrance of price to be a decimal field similar in structure to the price field of the Good model.

3

Thaks for your answer
yes you are right
so should i define BuyBasket price as a normal decimal field?

4

To add on @KenWhitesell i also think you should consider to properly design you models/tables. Here are some modification have made if you can take a look

BRANCH_TYPES = [
    ("MAIN_BRANCH", "MAIN_BRANCH"),
    ("SUB_BRANCH", "SUB_BRANCH"),
]



class Branch(models.Model):
    branch_name = models.CharField(default='', max_length=9000)
    branch_type = models.CharField(default='', choices=BRANCH_TYPES, max_length=9000, null=True)

class Good(models.Model):
    branch = models.ForeignKey(Branch, on_delete=models.CASCADE,related_name = "good_branch", verbose_name='کد دسته اصلی', default=0)
    goodproperties = models.OneToOneField(GoodProperties, on_delete=models.CASCADE,verbose_name='مشخصات کالا', null=True, blank=True)
    goodspecifications = models.OneToOneField(GoodSpecification, on_delete=models.CASCADE,verbose_name='معرفی کالا', default=0, null=True, blank=True)    
    image = models.ImageField(upload_to='photos/%Y/%m/%d', null=True, blank=True, verbose_name='تصویر کالا')
    quantity = models.PositiveIntegerField(default=0, verbose_name='تعداد موجود')
    price = models.DecimalField(decimal_places=0, max_digits=12, default=0,verbose_name='قیمت کالا')
    discount = models.SmallIntegerField(null=True, blank=True, verbose_name='میزان تخفیف')
    seller = models.ManyToManyField('Seller', verbose_name='کد فروشنده')
    
       
    
class BuyBasket(models.Model):
    customer = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, blank=True, null=True,       verbose_name='کد مشتری')
    quantity = models.PositiveIntegerField(verbose_name='تعداد')
    good = models.ForeignKey(Good, on_delete=models.CASCADE, default=0, verbose_name='قیمت کالا') # type: ignore
    total_price = models.DecimalField(decimal_places=0, max_digits=16, default=0, verbose_name='مبلغ کل سفارش') # type: ignore
    change_to_order = models.BooleanField(blank=True, null=True, verbose_name='تبدیل به سفارش')

Changes:-

  1. I introduce new model called Branch which will give you ability to dynamically add new sub-branch like subbranch1, subbranch2, subbranch3, subbranch4
  2. In BuyBasket i remove branches fields since good field is already linked to branch.
  3. The price on the BuyBasket model has no use since Good has its price
5

Thank you for your time spending for redefining models
it is really helpful and i learned from it

an other thing i though about ypur modifications is to add another field to Branch call it superbranch
because every branch with bigger number in last part of its name (subbranch2 has a bigger number compare to subbranch1 and …) is a subset of branch with smaller number in last part of its name
so for example subbranch1 is superbranch for subbranch2 and subbranch2 is subset of subbranch1