如何在Django中保存具有相同模型但具有不同数据的数据

Question

I'm working on a mini project which uses Django 1.8. The aim is to build a small billing app. So, I've created two models, Bill and Product, as follows.

#bill/models.py

class Bill(models.Model):
  date_of_issue = models.DateField()
  name = models.CharField(max_length=50, default="N/A", null=True)
  address = models.CharField(max_length=150, default="N/A", null=True)
  created = models.DateTimeField(auto_now_add=True)
  modified = models.DateTimeField(auto_now=True)

def __str__(self):
    return "{} {}".format(self.input_name, self.date_of_issue)

class Product(models.Model):
  bill = models.ForeignKey(Bill, on_delete=models.CASCADE)
  description = models.CharField(max_length=100, default="N/A")
  quantity = models.IntegerField(default=0)
  total = models.IntegerField(default=0)

By seeing the model, you can tell that my approach is to create Bill and Product tables and connect the Product to Bill via ForeignKey. Now, the thing is that a single bill will contain at least one product. If there are more than one product, how should I write my views in views.py . I'm a beginner in the Django development. If a Bill contains a single Product then I can write its view. But how can I store multiple Product which have different data and storing it in database.

For Example

The user will enter the name and address of the customer. Then the user will enter the details of products. Now I want to generate the Product modelform more than once (depends upon the number of products added by user). How can I accomplish this ?

Answer 1

Assuming

1) multiple products can be bought at once (and thus be part of one bill) and

2) one product can be bought multiple at any time (and thus be part of many bills)

a simple foreign key is the wrong modelling attempt. Instead of a m:1 relation you need a m:n relation - and thus a ManyToManyField . With a ManyToManyField you can add multiple products to one bill or have mutiple products added to multiple bills. In django-admin it's useful (and I recommend it) to put ManyToManyFields as filter_horizontal which eases the use of this field.

Plus, django will automatically resolve your m:n relation with an additional third database table, so you don't need to take care of this.