When I order over a ManyToMany relationship, certain records will not
appear. The record which disappears changes depending on the order by
which I sort it. Specifically:
>>> Listing.objects.order_by("book__courses")
gives me Listings with id's (5, 1, 3, 5, 2, 4), and
>>> Listing.objects.order_by("-book__courses")
gives me Listings with id's (6, 4, 5, 2, 5,1)
There is nothing wrong with the ordering. The problem is that a record
is disappearing in the ordering process. My pertinent models are
below. Any clues?
-------------------------------------------------------
class Course(models.Model):
"""
Basic course data
"""
division = models.CharField(max_length=5)
number = models.CharField(max_length=4)
title = models.CharField(max_length=250)
class Meta:
ordering = ('division', 'number')
def code(self):
return "%s %s" % (self.division, self.number)
def __unicode__(self):
return self.code()
class Book(models.Model):
"""
Information on a book (as opposed to a particular copy of it)
The attributes should be self-explanatory
"""
title = models.CharField(max_length=250)
author = models.CharField(max_length=70)
barcode = models.CharField(max_length=50)
edition = models.PositiveSmallIntegerField()
courses = models.ManyToManyField(Course)
def __unicode__(self):
return self.title
def course_codes(self):
"""
returns a list of courses in the form
course1, course2, course3
"""
course_list = ""
for course in self.courses.all():
course_list += "%s, " % course.code()
# [:-2] takes off the trailing comma and space
return course_list[:-2]
def title_list(self):
return self.author
class Listing(models.Model):
"""
For when a student lists a particular copy of a book.
Keeps track of
* when and who listed (is selling) it
* if and who is currently holding it
* when it was last put on hold
* when it finally got sold
* whether the listing is flagged for deletion or not
"""
STATUS_CHOICES = (
(u'F', u'For Sale'),
(u'M', u'Missing'),
(u'O', u'On Hold'),
(u'P', u'Seller Paid'),
(u'S', u'Sold'),
(u'T', u'To Be Deleted'),
(u'D', u'Deleted'),
)
book = models.ForeignKey(Book)
list_date = models.DateTimeField('Date Listed', auto_now_add=True)
seller = models.ForeignKey(User, related_name="selling")
sell_date = models.DateTimeField('Date Sold', blank=True,
null=True)
holder = models.ForeignKey(User, related_name="holding",
blank=True, null=True)
hold_date = models.DateTimeField('Date Held', blank=True,
null=True)
price = models.DecimalField(max_digits=7, decimal_places=2)
status = models.CharField(max_length=1, choices=STATUS_CHOICES)
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