CODEWITHSUNDEEP
pythondjangosortingdjango-modelsdjango-queryset
sgarza62
sgarza62

Reputation: 6238

Django: Ordered list of model instances from different models?

Users can upload three different types of content onto our site: image, video, audio. Here are the models for each type:

class ImageItem(models.Model):
    user = models.ForeignKey(User)
    upload_date = models.DateTimeField(auto_now_add=True)
    image = models.ImageField(upload_to=img_get_file_path)
    title = models.CharFiled(max_length=1000,
                             blank=True)

class VideoItem(models.Model):
    user = models.ForeignKey(User)
    upload_date = models.DateTimeField(auto_now_add=True)
    video = models.FileField(upload_to=vid_get_file_path)
    title = models.CharFiled(max_length=1000,
                             blank=True)

class AudioItem(models.Model):
    user = models.ForeignKey(User)
    upload_date = models.DateTimeField(auto_now_add=True)
    audio = models.FileField(upload_to=aud_get_file_path)
    title = models.CharFiled(max_length=1000,
                             blank=True)

I have a page called library.html, which renders all the items that a user has uploaded, in order from most recently uploaded to oldest uploads (it displays the title and upload_date of each instance, and puts a little icon on the left symbolizing what kind of item it is).

Assuming it requires three separate queries, how can I merge the three querysets? How can I make sure they are in order from most recently uploaded?

Upvotes: 4

Views: 2749

Answers (3)

acjay
acjay

Reputation: 36491

As an alternative, you can use multi-table inheritance and factor common attributes into a superclass model. Then you just order_by upload date on the superclass model. The third-party app django-model-utils provides a custom manager called Inheritance manager that lets you automatically downcast to the subclass models in your query.

from model_utils.managers import InheritanceManager

class MediaItem(models.Model):
    objects = InheritanceManager()

    user = models.ForeignKey(User)
    upload_date = models.DateTimeField(auto_now_add=True)
    title = models.CharFiled(max_length=1000,
                             blank=True)

class ImageItem(MediaItem):
    image = models.ImageField(upload_to=img_get_file_path)

class VideoItem(MediaItem):
    video = models.FileField(upload_to=vid_get_file_path)

class AudioItem(MediaItem):
    audio = models.FileField(upload_to=aud_get_file_path)

Then, your query is just:

MediaItem.objects.all().order_by('upload_date').select_subclasses()

This way, you get what you want with one just query (with 3 joins). Plus, your data is better normalized, and it's fairly simple to support all sorts more complicated queries, as well as pagination.

Even if you don't go for that, I'd still use abstract base class inheritance to conceptually normalize your data model, even though you don't get the database-side and ORM benefits.

Upvotes: 5

sgarza62
sgarza62

Reputation: 6238

Referencing the question, this is the exact solution I used. Influenced by monkut's answer and the top answer from Frantzdy's link in his comment (thanks guys).

from itertools import chain
from operator import attrgetter

images = ImageItem.objects.filter(user=user)
video = VideoItem.objects.filter(user=user)
audio = AudioItem.objects.filter(user=user)
result_list = sorted(chain(images, video, audio),
                     key=attrgetter('upload_date'),
                     reverse=True)

Upvotes: 1

monkut
monkut

Reputation: 43832

attrgetter can be used to pull out attributes of objects that you may want to key a sort by.

from operator import attrgetter

results = []
results.extend(list(AudioItem.objects.filter(...)))
results.extend(list(VideoItem.objects.filter(...)))
results.extend(list(ImageItem.objects.filter(...))
results.sort(key=attrgetter("upload_date")

Upvotes: 0

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