queryset_puzzle.py

# -*- coding: utf-8 -*-

from __future__ import (absolute_import, division, print_function,
    unicode_literals)

from django.db import models

class Product(models.Model):
    """ Store products """
    name = models.CharField(max_length=50)


class Locality(models.Model):
    """ Store localitys """
    name = models.CharField(max_length=50)


class Supply(models.Model):
    """ A product and a locality make a supply with N items """
    product = models.ForeignKey(Product, related_name='supply')
    locality = models.ForeignKey(Locality, related_name='supply')
    item_amount = models.PositiveInterField()


class Price(models.Model):
    """
    Price is used to calculate stock price at end of month, it changes when
    new items is added. We always have 1 for each month.
    """
    supply = models.ForeignKey(Supply, related_name='prices')
    price = models.DecimalField(default=0, max_digits=8, decimal_places=2)
    year = models.PositiveInterField()
    month = models.PositiveInterField(min_value=1, max_value=12)


class Ticket(models.Model):
    """
    Ticket is a simple class to centralize tickets for 'office supplies',
    'post office', and other systems.
    A new ticket is created every time someone want something from some system.
    """
    date_created = models.DateTimeField(auto_create_now=True, editable=False)
    date_finished = models.DateTimeField(editable=False, null=True, default=None)
    user = models.ForeignKey(User, related_name='tickets')


class TicketItem(models.Model):
    """
    Since Tickets are used by many other systems (ex, post office), this model
    is the link between Tickets and Supplies.
    """
    ticket = models.ForeignKey(Ticket)
    supply = models.ForeignKey(Supply)
    amount_out = models.PositiveInterField()

"""
I need to get every ticket item requested with it price, so fields that I need,
starting from TicketItem, is:

ticket id, ticket date created, ticket date finished, supply price for same date
of ticket date finished, supply localityuntitled, supply product

With following query I get everything, except price:

TicketItem.objects.values_list('ticket__id', 'ticket__date_created',
    'ticket__date_finished', 'supply__product__name', 'supply__locality__name')

Unfortanately, using F dont help me:

TicketItem.objects.filter(supply__prices__year=F('ticket__date_created__year')\
    .values_list('ticket__id', 'ticket__date_created', 'ticket__date_finished',
        'supply__product__name', 'supply__locality__name')

How I can do it with django offers?
"""