模型冗余Django表？

Question

I am working to figure out the model for a Django project: an app to track Books .

Among other fields, every Book has either/both a Printer and a Publisher , which are basically identical. So, here's how it stands:

class Book(models.Model):
    title     = models.CharField(max_length=100)
    printer   = models.ForeignKey('Printer')
    publisher = models.ForeignKey('Publisher')

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

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

It seems to me this is bad database form: it's not DRY. In addition, quite often, a Book might be printed by a firm which publishes the same or another book: in other words, the tables can overlap. So, the two models Printer and Publisher should really be combined, while they need to remain distinct in the admin.

My question: how best to do this? Should I create another model, Firm , and create one-to-one relationships between it and Printer / Publisher ?

Answer 1

The Django way to handle that is to create an Abstract Base Model . This is the DRY way to create your models. Here is the code:

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

    class Meta:
        abstract = True

class Printer(BaseModel):
    pass

class Publisher(BaseModel):
    pass

This will allow you to specify redundant fields only once. Also, if you need to add any extra fields to one model, just add them instead of using pass .