Django:如何创建在外壳中有ManyToManyField的对象？

from django.db import models

class Item(models.Model):
    name = models.CharField(max_length=100)

class Shell(models.Model):
    name = models.CharField(max_length=100)
    items = models.ManyToManyField(Item)

python manage.py makemigrations
python manage.py migrate

from django.shortcuts import render, redirect
from .forms import ShellForm

def create_shell(request):
    if request.method == 'POST':
        form = ShellForm(request.POST)
        if form.is_valid():
            shell = form.save()
            return redirect('shell_detail', pk=shell.pk)
    else:
        form = ShellForm()
    return render(request, 'create_shell.html', {'form': form})

<form method="post">
  {% csrf_token %}
  {{ form.as_p }}
  <input type="submit" value="Create Shell">
</form>