Django OneToMany

Question

I'm implementing a small e-shop application in django. My question concerns modelling an Order with many OrderLines: How to model the Order to OrderLines relationship with the OrderLines accessible directly from the Order, i.e.

Order
    def addOrderLine
    def allOrderLines

I want to access the OrderLines from the Order and not have to get them from the db directly. Django offers the possibility to define ForeignKeys, but this doesn't solve my problem, because I'd have to define the following:

class OrderLine(models.Model):
   order = models.ForeignKey(Order)

With this definition I'd have to fetch the OrderLines directly from the db and not through the Order.

I'm might use this definition and provide methods on the Order level. This, however, doesn't work because if I define the Order above the OrderLine in the models.py file, the Order doesn't see the OrderLines

Answer 1

You want a ForeignKey to Order from OrderLine. Something like this:

from django.db import models

class Order(models.Model):
    created_at = models.DateTimeField(auto_now_add=True)

class OrderLine(models.Model):
    order = models.ForeignKey(Order, related_name='orderlines')
    name = models.CharField(max_length=30)

    def __unicode__(self):
        return self.name

# Create a new order in the DB:
>>> order = Order.objects.create()
# Add a few items to this order:
>>> order.orderlines.create(name='Candied Yams')
<Candied Yams>
>>> order.orderlines.create(name='Minty loin of Lamb')
<Minty loin of Lamb>
# Get all items for this order:
>>> order.orderitems.all()
[<Candied Yams>, <Minty loin of Lamb>]

This is pretty well documented behavior :)