我如何为 Django 中的类别制作好的模型？

Question

im trying to make an online menu. i want to make a category, sub category and items that goes in one of those.

I mean, an item can be on a category like "sushi" -> nameofsushi, or be in a sub category like sushi -> avocado rolls -> nameofsushi.

i have something like this in my models.py but is there a better way to do it?

class Category(models.Model):
    name = models.CharField(max_length=200)
    description = models.TextField(max_length=500, verbose_name='Descripción', blank=True, null=True)
    parent = models.ForeignKey('self', related_name='children', null=True, blank=True, on_delete=models.CASCADE)
    
    def __str__(self):
        return 'Category: {}'.format(self.name)

class MenuItem(models.Model):
    name = models.CharField(max_length=200)
    image = models.ImageField(upload_to='menu_images/', null=True, blank=True)
    description = models.TextField(blank=True, null=True)
    price = models.DecimalField(max_digits=6, decimal_places=0)
    other_Price = models.DecimalField(max_digits=6, decimal_places=0, null=True, blank=True)
    categories = models.ManyToManyField('Category', related_name='item', null=True, blank=True)
    
    def __str__(self):
        return 'MenuItem: {}'.format(self.name)

Answer 1

You need to carefully think about your model design. The way you have designed categories allows you to have unlimited sub-categories. Do you really need that flexibility? Because it comes at the cost of complexity. Think about how you will be interacting with the models.

With your current design, it would be challenging to render in a Django template without preprocessing it in Python using some gnarly recursion, because you have no way apriori to know how many nested sub categories you have. You could have sub-category, sub-sub-category, sub-sub-sub-category and so on.

Also, querying your models will be complicated. Say you have 'Cat1'->'Sub-cat1'->'Sub-sub-cat1'->'menuitem1' . How do you find all menu items that are a descendant of 'sub-cat1 '? All I can think of is MenuItem.objects.filter(parent__parent=subcat1_obj) . Not very Pythonic or clear to a reader. And you run into problems as you dont know how many layers of sub-categories you have.

Or how do you get just the menu categories? Category.objects.filter(parent=None) . Its not obvious from this code what we are talking about.

I would, if your use-case allows it, simplify your model design in this way:

class MenuCategory(models.Model):
    category = models.ForeignKey(Category, ...)
    ...

class MenuSubCategory(models.Model):
    menu_category = models.ForeignKey(MenuCategory, ...)
    ...

class MenuItem(models.Model):
    menu_categories = models.ManyToManyField(MenuCategory, ...)
    menu_subcategories = models.ManyToManyField(MenuSubCategory, ...)
    ...

Now rendering your models in a template would be straight forward (given context['menu_categories'] = MenuCategory.objects.all() ):

{% for cat in menu_categories %}
  {% for item in cat.menuitem_set.all %}
    {{ item }}
  {% endfor %}
  {% for subcat in cat.menusubcategory_set.all %}
    {% for item in subcat.menuitem_set.all %}
      {{ item }}
    {% endfor %}
  {% endfor %}
{% endfor %}

Now querying your models will also be more clear. You could also if needed add a Menu model and have different menus.