Django/Python: How to group queryset results by date?

Question

I have a model for image uploads, that looks something like this:

from django.db import models
from django.contrib.auth.models import User
import datetime

class ImageItem(models.Model):
    user = models.ForeignKey(User)
    upload_date = models.DateTimeField(auto_now_add = True)
    last_modified = models.DateTimeField(auto_now = True)
    original_img = models.ImageField(upload_to = img_get_file_path)

I want to query all instances of ImageItem that belong to a particular user, and group them according to date uploaded. For example, for some user, I want a group for April 9 2013, another for April 12 2013, etc. (assuming that they uploaded one or more images on those dates).

I'm thinking I run a simple query, like,

joes_images = ImageItem.objects.filter(user__username='joe')

But then how could I group them by day published? (assuming he did not publish every day, only on some days)

The function would have to return all the groups of images.

Have you read this question? http://stackoverflow.com/questions/629551/how-to-query-as-group-by-in-django — Henrik Andersson, Apr 13 '13 at 05:01
No, I hadn't, and that definitely solves the first half of my question. Here, the `upload_date` field is a datetime.datetime object, which means no two upload_date values are the same. I would like to group only according to date, not time. How would I do that? — sgarza62, Apr 13 '13 at 05:29
I think you have to use `.extra()` for that, you can't `.order_by()` on a datetimefield unfortunately :( — Henrik Andersson, Apr 13 '13 at 05:31
You could however convert it to a DateTimeField instead and be done with it. Ie. have one field for grouping on and one field for doing whatever else on. (This is a bit superflous but it'd work) — Henrik Andersson, Apr 13 '13 at 05:37
Ref http://stackoverflow.com/a/2283913/165603 , you could do it in `extra` by typing cast datetime to date. If applicable, writing a SQL in `raw()` is more clear. — okm, Apr 13 '13 at 10:25

score 4 · Accepted Answer · answered Apr 13 '13 at 11:41

why don't you do as following?

joes_images = ImageItem.objects.filter(user__username='joe')  # your code
upload_dates = set([(i.year, i.month, i.day) for i in joes_images])  # set of upload_date
joes_images_separated = dict([(d, []) for d in upload_dates])
for d in upload_dates:
    for i in joes_images:
        if (i.year, i.month, i.day) == d:
            joes_images_separated[d].append(i)

Here, upload_dates is a set of dates in joes_images and you get joes_images_separated as a dict (keys are dates, values are lists of joes_images for each date).

I'm sorry for a little dirty code. I think this works. for your information.

You do not need 2 for loops. Get rid of `for d in upload_dates:` and the if statement and just construct the date key `d` for every image in `joes_images` — roob, Nov 11 '16 at 00:01

Django/Python: How to group queryset results by date?

1 Answers1