Trying to establish a realtion Between model tables in Django.but iam getting error while insering values |foreign-key item must be an instance

Question

class User(AbstractUser):
    pass
class auction_list(models.Model):
    item_id=models.IntegerField(primary_key=True)
    item_name=models.CharField(max_length=64)
    owner=models.CharField(max_length=64)
    image=models.CharField(max_length=128)
    def __str__(self):
        return f"{self.item_id}:{self.owner}{self.item_name}"
class bid(models.Model):
    item_id=models.ForeignKey(auction_list,on_delete=models.CASCADE,related_name="currentbid")
    bid=models.IntegerField(max_length=16)
    user=models.CharField(max_length=64)
    def __str__(self) :
        return f"{self.item_id}{self.bid}{self.user}"

and when i try to inser the valules i get this error

inseritions i tried to do:

In [16]: a3=auction_list(item_id=3,item_name="keyboard",owner="alex" )

In [17]: a3.save()
In [18]: a3
Out[18]: <auction_list: 3:alexkeyboard>
In [20]: b1=bid(item_id=3,bid=100,user="alex")

and the error i get is

In [20]: b1=bid(item_id=3,bid=100,user="alex")
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-20-6befcb719aa3> in <module>
----> 1 b1=bid(item_id=3,bid=100,user="alex")

~\AppData\Local\Programs\Python\Python39\lib\site-packages\django\db\models\base.py in __init__(self, *args, **kwargs)
    483                 # checked) by the RelatedObjectDescriptor.
    484                 if rel_obj is not _DEFERRED:
--> 485                     _setattr(self, field.name, rel_obj)
    486             else:
    487                 if val is not _DEFERRED:

~\AppData\Local\Programs\Python\Python39\lib\site-packages\django\db\models\fields\related_descriptors.py in __set__(self, instance, value)  
    213         # An object must be an instance of the related class.
    214         if value is not None and not isinstance(value, self.field.remote_field.model._meta.concrete_model):
--> 215             raise ValueError(
    216                 'Cannot assign "%r": "%s.%s" must be a "%s" instance.' % (
    217                     value,

ValueError: Cannot assign "3": "bid.item_id" must be a "auction_list" instance.

can some one help me understand wht is the problem here and how can i resolve these

Answer 1

Django automatically adds a …_id suffix to ForeignKey s to define a field that will refer to the primary key (or another unique field) of another model.

You thus should define your model as:

class bid(models.Model):
    =models.ForeignKey(
        auction_list,
        on_delete=models.CASCADE,
        related_name='currentbid'
    )

You can then create Bid objects with:

Bid.objects.create(
    ,
    # …
)

or with:

Bid.objects.create(
    ,
    # …
)

---

Note : Models in Django are written in PascalCase , not snake_case , so you might want to rename the model from bid to Bid .

Answer 2

You are trying to insert an Integer when you should be inserting that Table's instance (or queryset, in other words) to the value of that item_id field in Bid Table.

What I mean is, instead of b1=bid(item_id=3,bid=100,user="alex") , you should do b1=bid(item_id=a3, bid=100, user="alex") and then .save().

If you don't want to insert the Queryset and only want to include the Integer, you can modify your code to b1=bid(item_id_item_id=3, bid=100, user="alex") and it will work just fine.