Django Form: form with ForeignKey - django

Question

I'm making online shopping mall using Django(1.9.7) framework.
I think that showing codes is much easier than explaining in text.
models.py
class Product(TimeStampedModel):
name = models.CharField(max_length=120, unique=True)
slug = models.SlugField(null=True, blank=True)
description = models.TextField(max_length=400, blank=True)
is_active = models.BooleanField(default=True)
def __str__(self):
return self.name
class Variation(TimeStampedModel):
COLOR_CHOICES = (
('black', '흑백'),
('single', '단색'),
('multi', '컬러'),
)
price = models.DecimalField(
decimal_places=0,
max_digits=15,
blank=True,
null=True,
)
product = models.ForeignKey(Product)
color = models.CharField(
max_length=10,
choices=COLOR_CHOICES,
)
is_active = models.BooleanField(default=True)
class Meta:
unique_together = (('product', 'color'))
def __str__(self):
return str(self.product) + ' - ' + self.get_color_display()
I create form in my product_detail view and pass it as context data to template.
views.py
class ProductDetailView(DetailView):
model = Product
context_object_name = "product"
def get_context_data(self, *args, **kwargs):
context = super().get_context_data(*args, **kwargs)
product = self.get_object()
context['cartitem_form'] = CartItemForm(product)
return context
What I want to do through form:
I want to show variations only related with given product. So I pass product as argument of form in view and save this product. And I'm trying to set the variation queryset through ModelChoiceField:
class CartItemForm(forms.ModelForm):
variation = forms.ModelChoiceField(
queryset=Variation.objects.filter(product=self.product)
)
class Meta:
model = CartItem
fields = (
'variation',
'width',
'height',
'quantity',
)
def __init__(self, *args, **kwargs):
self.product = kwargs.pop('product')
super().__init__(*args, **kwargs)
def save(self):
cart_item = super().save(commit=False)
cart_item.save()
return cart_item
but it doesn't work. How can I implement this?