Django设计模型：项目/库存/用户

Question

I would like to ask some advice on Modeling a specific model behavior. Basically I have a model Item. It describes the name and description of an item.

I have a inventory, which should hold a "List" of items, considering the quantity of each item should be specified in the inventory.

Each User should have one unique inventory.

Here's what I'm trying to do:

class User(models.Model):
    name = models.CharField(max_length=100)
    invetory =models.ForeignKey(inventory,on_delete=models.CASCADE)


class item(models.Model):
    name =models.CharField(max_length=40)
    description = models.TextField(max_length=200)
    value = models.FloatField()

class inventory(models.Model):
?

I'm not sure if this is the right approach.

Answer 1

class User(models.Model):
    name = models.CharField(max_length=100)


class Inventory(models.Model):
   user = models.OneToOneField(User,on_delete=models.CASCADE)

class Item(models.Model):
    name =models.CharField(max_length=40)
    description = models.TextField(max_length=200)
    value = models.FloatField()
    invetory =models.ForeignKey(Inventory,on_delete=models.CASCADE)

This should work as per your specification. We have tied up inventory to a user and each item will have a foreign key to Inventory table.

Now you can do

1. To access inventory you can do `user.inventory`
2. To get a list of items `user.inventory.item_set` 
3. You should use the `post_save` signal to create the inventory object. 

Answer 2

class inventory(models.Model):
    user = models.ForeignKey(User, default=User.objects.first())
    item = models.ForeignKey(Item, default=Item.objects.first())
    count = models.IntegerField(default=0)

I think this would make a better design.

Answer 3

You should use many-to-many relations. First of all you should delete the FK from the User model. Then create a separate model for items and finally link many users to many items (one user can handle multiple items and one item can belong to multiple users). Something like that:

class User(models.Model):
    name = models.CharField(max_length=100)


class item(models.Model):
    name =models.CharField(max_length=40)


class inventory(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    item = models.ForeignKey(item, on_delete=models.DO_NOTHING)
    quantity = models.FloatField()

PS Class names should use PascalCase convention https://www.python.org/dev/peps/pep-0008/?#class-names