save() prohibited to prevent data loss due to unsaved related object 'user' - django

Question

i am trying to save data in a table when a user click the checkout button of add to cart but it is showing me the above mention error i am unable to understand and one more thing is happening when i logout my the cart which i saved also got erased is it shomehow related to that i don't know
here is my views.py for checkout button
class Checkout(View):
def post (self, request,):
user = request.session.get('user')
ids = (list(request.session.get('cart').keys()))
sections = Section.get_sections_by_id(ids)
for section in sections:
order = Order(user = User(id=user),
section = section,
price = section.price,
)
order.save()
my views.py for cart.html
class Cart(View):
def get (self, request):
ids = (list(request.session.get('cart').keys()))
sections = Section.get_sections_by_id(ids)
print(sections)
return render(request, 'cart.html', {'sections': sections})
my urls.py
urlpatterns = [
path('cart/', Cart.as_view(),name='cart'),
path('Check-Out/', Checkout.as_view(),name='checkout'),
]
my cart.html
{% extends 'base.html' %}
{% load static %}
{% load cart %}
{% load custom %}
{% block head %}
<link rel="stylesheet" href="{% static 'css/cart.css' %}">
{% endblock %}
{% block content %}
<div class="container jumbotron">
<section>
<h1>My cart</h1>
<table class="table">
<thead>
<tr>
<th scope="col">S.no</th>
<th scope="col">Subject</th>
<th scope="col">Section</th>
<th scope="col">Teacher</th>
<th scope="col">Duration</th>
<th scope="col">Price</th>
</tr>
</thead>
{% for section in sections%}
<tbody style="margin-bottom: 20px;">
<tr>
<th scope="row">{{forloop.counter}}</th>
<td>{{section.subject.name}}</td>
<td>{{section.title}}</td>
<td>{{section.teacher}}</td>
<td>{{section.content_duration}}</td>
<td>{{section.price|currency}}</td>
</tr>
</tbody>
{% endfor %}
<tfoot>
<tr>
<th> Total</th>
<th></th>
<th></th>
<th></th>
<th></th>
<th>{{sections|total_price:request.session.cart|currency}}</th>
</tr>
<hr>
</tfoot>
</table>
<button type="button" data-toggle="modal" data-target="#exampleModal" style="float: right; margin-left:5px" class="btn btn-outline-primary">Check Out</button>
<button type="button" style="float: right; margin-left:5px" class="btn btn-info">Back To Site</button>
</tfoot>
</section>
</div>
<!-- Modal -->
<div class="modal fade" id="exampleModal" tabindex="-1" aria-labelledby="exampleModalLabel" aria-hidden="true">
<div class="modal-dialog">
<div class="modal-content">
<div class="modal-header">
<h5 class="modal-title" id="exampleModalLabel">Please Verify</h5>
<input type="button"class="btn-close btn-link" style="text-decoration:none; border:none; font-size:20px;" data-dismiss="modal" aria-label="Close" value="X">
</div>
<div class="modal-body">
<form action="{% url 'transactions:checkout' %}" method="Post">
{% csrf_token %}
<input type="submit" class="btn float-right btn-primary" value='Go Ahead'>
</form>
</div>
</div>
</div>
</div>
{% endblock %}
and my models.py
class Order(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE,)
section = models.ForeignKey(Section, on_delete=models.CASCADE )
price = models.FloatField(blank=False)
update_at = models.DateTimeField(auto_now=True, editable=False)
def placeorder(self):
self.save()
please help if you can an

Answer 1

The issue caused by this line:
order = Order(user = User(id=user)
Using User(id=user) means you want to create an unsaved User and use it in an unsaved Order and then saving the order, but this will not work because you haven't saved the User yet, as mentioned by the error.
You can just simply just use the existing user in the order like this:
order = Order(user=user, section=section, price=section.price)
order.save()