尝试在 Django 中保存模型表单时，为什么会出现“外键不匹配”？

我正在尝试在 Django 中保存一个模型表单的实例。我已经设置了一个模板来输入信息到表单和一个视图来处理保存。表单验证正常，但在尝试保存时会生成外键不匹配错误。我在这里做错了什么？

我正在运行 Django 2.0.0。我已经尝试添加和删除 primary_key 选项而没有任何运气并删除我的 sqlite 数据库，清除所有 pycache，然后再次迁移。问题仍然存在。

#models.py
from django.db import models
import uuid
from users.models import Company, CustomUser
from delivery import settings

class Location(models.Model):
    location_id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    address = models.CharField(max_length = 120)
    date_added = models.DateField(auto_now_add = True)

class Shipment(models.Model):
    date_created = models.DateField(auto_now_add=True)
    sender_company = models.ForeignKey(Company, on_delete = models.PROTECT, related_name='sender')
    receiver_company = models.ForeignKey(Company, on_delete = models.PROTECT, related_name='receiver')
    origin = models.ForeignKey(Location, on_delete = models.SET_DEFAULT, default = 'Location no longer active.', related_name='origin')
    destination = models.ForeignKey(Location, on_delete = models.SET_DEFAULT, default = 'DESTINATION UNKNOWN', related_name='destination')
    expected_arrival = models.DateField()
    weight = models.FloatField()
    current_handler = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete = models.SET_DEFAULT, default = 'UNKNOWN')
    shipment_id = models.UUIDField(unique=True, primary_key = True, default=uuid.uuid4, editable=False)

#forms.py
from django import forms
from .models import Location, Shipment

class LocationRegisterForm(forms.ModelForm):

    class Meta:
        model = Location
        fields = '__all__'      

class CreateShipment(forms.ModelForm):

    class Meta:
        model = Shipment
        exclude = ['current_handler', 'shipment_id']

    def clean_expected_arrival(self):
        expected_arrival = self.cleaned_data['expected_arrival']
        date_created = self.cleaned_data['date_created']
        if expected_arrival < date_created:
            raise ValidationError('Expected arrival date cannot be in the past.')
        return expected_arrival

#views.py
from django.shortcuts import render, redirect
from .forms import CreateShipment, LocationRegisterForm
from users.permissions import group_required

@group_required('delivery_employee')
def new_shipment(request):
    if request.method == 'POST':
        form = CreateShipment(request.POST)
        if form.is_valid():
            temp_form = form.save(commit=False)
            current_user = request.user
            temp_form.current_handler = current_user
            temp_form.save()
            return redirect('dash-home')
        else:
            return render(request, 'shipments/new-shipment.html', {'form':form})
    form = CreateShipment()
    return render(request, 'shipments/new-shipment.html', {'form':form})

@group_required('delivery_employee')
def add_location(request):
    if request.method == 'POST':
        form = LocationRegisterForm(request.POST)
        if form.is_valid():
            form.save()
            return redirect('new-shipment')
        else:
            return render(request, 'shipments/location-register.html', {'form':form})
    form = LocationRegisterForm()
    return render(request, 'shipments/location-register.html', {'form':form})

我收到错误消息：

File "C:\Python34\lib\site-packages\django\db\backends\sqlite3\base.py", line 303, in execute
    return Database.Cursor.execute(self, query, params)
django.db.utils.OperationalError: foreign key mismatch - "shipments_shipment" referencing "shipments_location"

谢谢！