How to pass a <select> in a View using Django - django

Question

I was trying to make a cart system in Django and wanted to pass Size and the Quantity of product as <Select>
input in View.
My Template have :
<ul class="list-unstyled">
Select Size:
<select name="sizes">
{% for size in product.sizes.all %}
<li class="list-item list-inline-item"><option value="{{size.nameSize}}">{{size.nameSize}}</option> </li>
{% endfor %}
</select>
</ul>
This is how it looks :
But when i Submit it using the Add to Cart Button i get error:
This is the code in the view:
def add_item(request,pk):
product = get_object_or_404(Product,pk=pk)
size = request.POST['sizes']
selectsize = Size.objects.get(nameSize=size)
user = request.user
usercart = Cart.objects.get(owner=user)
newitem = CartItems.objects.create(cart = usercart,product=product,size=selectsize)
items = usercart.cartitems
return render(request,'cart.html',{'cartitems':items})
I am trying to use the name of the size from the Template and compare the size name i have in the database for that product Using:
selectsize = Size.objects.get(nameSize=size)
I was able to get size with name 36 so i wanted to pass the value 36 from the template to the variable size using post.
But i get the error mentioned which i believe is because name for the <select> is common in all the <option>.
If i can either get an alternate way to do that or solve this error both type of solutions are welcomed.
*I am not using Django Forms because i don't know how to have django form display like i am displaying my products in cart and on the product page.
ANSWER
I was missing a submit button and was rather using a <a href="{% url 'add_item' product.pk %}>Add To Cart</a>" to submit the form which was not working.
Now i replaced it with <button class="btn btn-success" style="margin-top: 10px;" type="submit">Add To Cart New</button>
And the form Action is given the link i was trying to go to.
<form method="post" enctype="multipart/form-data" action="{% url 'add_item' product.pk %}">
A silly mistake on my side.
Thanks for the answers.

Answer 1

Expanding on what #Yevhenii M. said, and talking particularly about the MultiValueDictKeyError:
This error happens when the given key (sizes in this case) is not found in the POST dict. This might be happening (i'm only guessing, since you didn't post the full html code), because you didn't put the corresponding <form> tag surrounding the select.
So, the final code would look something like:
<form action="url-to-send-form-data" method="POST">
{% csrf_token %}
<select name="sizes">
{% for size in product.sizes.all %}
<option value="{{size.nameSize}}">{{size.nameSize}}</option>
{% endfor %}
</select>
</form>
The {% csrf_token %} is needed in order to protect you against Cross Site Request Forgery attacks (more info: https://docs.djangoproject.com/en/2.2/ref/csrf/)
EDIT: Now that I take a closer look, the error message shows that the url is being called with a GET request (maybe because of trying to access to /item_added/1 straight from the browser's url). That is why django can't find the sizes key.
One common way to call the url via post, is as shown in the code snipet above, and adding a submit button to the html:
...
<button type="submit">Submit</button>
</form>

Answer 2

You don't need to use <ul> tag here.
You can write:
Select Size:
<select name="sizes">
{% for size in product.sizes.all %}
<option value="{{size.nameSize}}">{{size.nameSize}}</option>
{% endfor %}
</select>
and result will be the same.
Since you didn't specify that add_item(request, pk) works only by POST, then you can't expect that request.POST always will be presented.
Better write your code as this:
if request.POST:
# do something
And if you don't specify default value for your select in template, then sizeswill not be in your request.POST.
You can write like this just to be sure that you got some value:
request.POST.get('sizes', 'some_default_value')
Just because you get MultiValueDictKeyError you need to see what you get in request. Maybe you get QueryDict, then you need to extract first value. For example, see this SO question. For example, print your request.POST or check type.