Hi all,
Would appreciate some help on how to optimise the following piece of code.
I have two models, "invoice" and "invoice item". The invoice total is
calculated in invoice_total() by aggregation the sub_total and tax_total
from all invoice_items (see code below).
The problem I have is that even though I prefetch all the invoice_items in
the view, when invoice.invoice_total is called in a template 3 identical
queries will be run for each invoice. For example see some output from a
profile.
# All invoice items are prefetched correctly
SELECT ••• FROM `billing_invoice_item` WHERE
`billing_invoice_item`.`invoice_id` IN (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 51,
53, 54, 55, 56, 58, 59, 60, 61, 62, 65, 66, 67, 68, 69, 70, 72, 73, 74, 75,
76, 77, 78, 80, 81, 82, 84, 85, 87, 88, 89, 90, 91, 92, 93, 94, 96, 97, 98,
99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 113, 114, 115,
116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 128, 129, 130, 131,
132, 134, 135, 136, 137, 138, 140, 141, 142, 143, 144, 145, 146, 147, 148,
149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163,
164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178,
179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193,
194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208,
209, 210, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224,
225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239,
240, 241, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255,
256, 257, 258, 259, 260, 261, 262, 263, 264, 265, 266, 267, 268, 269, 270,
271, 272, 273, 274, 275, 276, 277)
but then after this the table is queried 3 more times
SELECT ••• FROM `billing_invoice_item` WHERE
`billing_invoice_item`.`invoice_id` = 277
SELECT ••• FROM `billing_invoice_item` WHERE
`billing_invoice_item`.`invoice_id` = 277
SELECT ••• FROM `billing_invoice_item` WHERE
`billing_invoice_item`.`invoice_id` = 277
I'm using django 1.5 and my code is below.
Any thoughts?
#models.py
class Invoice(models.Model):
customer = models.ForeignKey(Customer)
:
:
:
def invoice_total(self):
invoice_total = self.invoice_item_set.aggregate(Sum('sub_total'),
Sum('tax_total'))
return str(round(invoice_total['sub_total__sum'], 2))
class Invoice_Item(models.Model):
invoice = models.ForeignKey('Invoice')
sub_total = models.DecimalField(blank=True, null=True, max_digits=9,
decimal_places=2)
tax_total = models.DecimalField(blank=True, null=True, max_digits=9,
decimal_places=2)
:
:
:
#views.py
def invoice(request):
invoices = Invoice.objects.all().prefetch_related('invoice_item_set',
'journals', 'journals__transaction_set',
'journals__transaction_set__account', 'customer')
return render_to_response('billing/invoices.html', {'invoices':
invoices,}, context_instance=RequestContext(request))
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