about cacade foreignkey in django admin page

My model is like below:

class Manufacturers(models.Model):
    name = models.CharField()

class Phones(models.Model):
    manufacturer = models.ForeignKey(Manufacturers)
    name = models.CharField()

class Prices(models.Model):
    phone = models.ForeignKey(Phones)
    price = models.DecimalFeild()

and I have registered them in the admin.py

My problem is: In django's admin interface, When I add a price, I can select a phone from the dropdown list, But there are so many phones, So I want to select the manufacturer at first, then select the phone from the manufacturer's phones. How can I make this. Thanks very much.

Solution

The term for this is "chained select menus".

There are a number of implementations in django. One that you may find useful is django-smart-selects.

Using django-smart-selects, this is how you would write up your models:

class Manufacturers(models.Model):
    name = models.CharField()

class Phones(models.Model):
    manufacturer = models.ForeignKey(Manufacturers)
    name = models.CharField()

class Prices(models.Model):
    phone = ChainedForeignKey(
        Phone, 
        chained_field="manufacturer",
        chained_model_field="manufacturer", 
        show_all=False, 
        auto_choose=True
    )
    price = models.DecimalField()

All that said, I wonder if you are implementing this in the best fashion.

It might be better to have Prices show up under the admin form for each phone. So instead of creating a price record and choosing the phone from a drop-down, you'd go into the record for that phone and add a price record. See django's documentation on InlineModelAdmin.