How to access foreign key depends on current active user in django

models.py

class Shop(models.model):
   shop_name = models.CharField(max_length=100, blank=True)
   slug = AutoSlugField()
   logo = models.ImageField(upload_to='restaurant_profile', blank=True)
   related_user = models.ForeignKey(User, on_delete=models.CASCADE)

class Product(models.Model):
    name = models.CharField(max_length=200)
    price = models.FloatField()
    slug = models.SlugField()
    created by = models.ForeignKey(Shop, on_delete=models.DO_NOTHING, default="")

forms.py

class AddProductForm(forms.ModelForm):
    name = forms.CharField(widget=TextInput(attrs={
        'class': 'form-control input-md',
        'style': 'width: 100%; display: inline;',
    }), required=True)

    price = forms.CharField(widget=TextInput(attrs={
        'class': 'form-control input-md',
        'style': 'width: 100%; display: inline;',
    }), required=True)
    category = forms.ModelChoiceField(queryset=ProductCategory.objects.all(), widget=Select(attrs={
        'class': 'form-control input-md',
        'style': 'width: 100%; display: inline;',
    }), required=True)
    class Meta:
        model = Product

        fields = [
            'name',
            'price',
            'category',
            'is_published',
            'created_by',
        ]

each shop has a related user, when a product is created, created_by field in Product models needs to fill with

created_by =  models.ForeignKey(Shop.filter(related_user = request.user)

how to assign this value when creating a product from this form
I am using class-based views

If you want to change the value of created_by in the form (not in the view, as you mentioned in the comments), you should pass the request, or even better, the request.user to the form and add that before saving:

<pre><code>class AddProductForm(forms.ModelForm):
#...

fields = [
    'name',
    'price',
    'category',
    'is_published',
    <b># 'created_by' Remove this</b>
]

def __init__(self, *args, **kwargs):
    <b>self.user = kwargs.pop('user')</b>
    super(UserProfileUpdateForm, self).__init__(*args,**kwargs)

def save(self, commit=True, *args, **kwargs):
    instance = super().save(commit=False, *args, **kwargs)
    <b>instance.created_by = self.user</b>
    instance.save()
    return instance</code></pre>

The final step is to include user in views, whenever you instantiate the form:

views.py:

my_form = AddProductForm(user=request.user)

in a form valid method in your views, you can add the logged in user as created by user, example shown is for a class based view

   def form_valid(self, form):
        form.instance.created_by = Shop.objects.get(related_user=self.request.user)
        valid_data = super(ProductCreateView, self).form_valid(form)
        return valid_data