How to access column from another table in list_display? - django

Question

I have these models:
class Orders(models.Model):
order_id = models.AutoField(primary_key=True)
user_id = models.IntegerField()
status = models.CharField(max_length=100)
created_at = models.CharField(max_length=100)
class Meta:
managed = False
db_table = 'orders'
class OrderItems(models.Model):
order_id = models.ForeignKey(Orders, models.DO_NOTHING)
quantity = models.IntegerField()
class Meta:
managed = False
db_table = 'order_items'
Now suppose I want list_display of the orders model to show the columns
order_id, user_id, status, created_at, quantity
I know I could do something like this:
class OrdersAdmin(admin.ModelAdmin):
list_display = ('id', 'user_id', 'status', 'created_at', 'get_quantity')
class Meta:
model = Orders
def get_quantity(self, obj):
result = XXX
return result.get('quantity')
get_quantity.short_description = 'Quantity'
admin.site.register(Order, OrderAdmin)
How can I access the information I need at XXX?

Answer 1

So you need to follow the reverse foreign key set for Orders (which btw should be named in singular).
So something like this:
orderitems = obj.orderitems_set.all()
sum = 0
for orderitem in orderitems:
sum = sum + orderitem.quantity
return sum
You can set related_name to rename the reverse set:
OrderItems(models.Model):
order_id = models.ForeignKey(Orders, models.DO_NOTHING, related_name="order_items")
and call it like order.order_items.all()
To order in OrdersAdmin:
def get_queryset(self,request):
qs = super(OrdersAdmin,self).get_queryset(request)
return qs.annotate(get_quantity=Sum('order_items__quantity'))
def get_quantity(self, obj):
return obj.order_items.all.aggregate(Sum('quantity'))
get_quantity.admin_order_field = 'get_quantity'