如何在创建具有多对多字段选择的Django模型对象时阻止表单提交，这在相关模型中不存在？

from django import forms
from .models import MyModel

class MyModelForm(forms.ModelForm):
    class Meta:
        model = MyModel
        fields = '__all__'

    def clean(self):
        cleaned_data = super().clean()
        m2m_field_data = cleaned_data.get('m2m_field')

        if not m2m_field_data:
            raise forms.ValidationError("请至少选择一个选项")

        return cleaned_data

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

def create_model(request):
    if request.method == 'POST':
        form = MyModelForm(request.POST)
        if form.is_valid():
            form.save()
            return redirect('success_url')
    else:
        form = MyModelForm()

    return render(request, 'create_model.html', {'form': form})