How can I define the ManyToManyField name in django?

I have this relationship

Class Item(models.Model):
   pass

Class Category(models.Model):
   items = models.ManyToManyField(Item)

I can define the field name as items for category and access it via category.items but I want to define a field name for Item too as item.categories rather than the default item.category

How can I achieve it?

See, ManyToManyField can't make reverse relationship with related model as python is interpreted language, so it can't read model class of previous one. Instead, you can do one thing ...

# models.py

class Item(models.Model):
    item_name = models.CharField(max_length=255, default="")

    def __str__(self):
        return self.item_name


class Category(models.Model):
    category_name = models.CharField(max_length=255, default="")
    items = models.ManyToManyField(Item)

    def __str__(self):
        return self.category_name

After that, you can list down your requirements in views.py file.

# views.py

def get_items_by_categories(request):
    
    # Here, you will receive a set of items ...
    
    get_categories = Category.objects.all()

    # Filter out items with respect to categories ...

    get_items_list = [{"category": each.category_name, "items": each.items} for each in get_categories]

    return render(request, "categories.html", {"data": get_items_list})

Iterate your items with categories in categories.html file.

{% for each in data %}
    {% for content in each %}
        {{content.category}}
        {% for item in content.items.all %}
            {{item.item_name}}
        {% endfor %}
    {% endfor %}
{% endfor %}

I hope this solution will help you ..

Thank You !

The thing about many to many field is not an actual field. If you take a look at the generated schema you wouldnt find the field as a column in either of the table. What happens in the back is django creates a ItemCatagory table.

class ItemCatagory(models.Model):
      item = modes.ForegnKeyField(Item, related_name="catagories", on_delete... )
      catagory = models.ForegnKeyField(Item, related_name="items", on_delete... )

catagory.items will give u the ItemCatagory RelatedObject and if u do catagoty.items.all() it will give u QuerySet[ItemCatagory]. so the default model.save() method woont add those rship. so u would have to overide save method on either of the models.

When you call Item.objects.create(), you need to omit the categories from the args. Then afterwards you can call set() to set the categories.

item = Item.objects.create()
item.categories.set(categories)

If you only have one category to add, you can call add() instead:

item = Item.objects.create()
item.categories.add(category)

Note: both add() and set() save the update to the database, so you don’t need to call item.save() afterwards.

Source: Many-to-Many relations

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