获取ManyToManyField的条目

我正在使用ManyToManyField并在表单上使用ModelMultipleChoice，我想获取条目，但我得到的只是 appname.Extra.none

models.py

class Extra(models.Model):

extra_n = models.CharField(max_length=200)
extra_price = models.IntegerField(default=0)

def __str__(self):
    return self.extra_n

class Meal(models.Model):

restaurant = models.ForeignKey(Restaurant, on_delete=models.PROTECT)
category = models.ForeignKey(MealCategory, on_delete=models.PROTECT)
name = models.CharField(max_length=500)
short_description = models.CharField(max_length=500)
image = models.ImageField(upload_to='meal_images/', blank=False)
price = models.IntegerField(default=0)
extras = models.ManyToManyField(Extra, related_name='extras')

def __str__(self):
    return self.name

forms.py

class MealForm(forms.ModelForm):

extras = forms.ModelMultipleChoiceField(widget=forms.CheckboxSelectMultiple(), queryset=Meal.extras)

class Meta:
    model = Meal
    exclude = ("restaurant",)

views.py

def restaurant_meal(request):

meals = Meal.objects.filter(restaurant = request.user.restaurant).order_by("-id")
return render(request, 'restaurant/meal.html', {"meals": meals})  

所需的输出是在restaurant_meal视图上显示添加的额外内容。