django query get last n records

user_342553 0
Viewed 104281

Lets say I am implementing a message stream, records sort by ID ascending order, each fetch request, I want to only allow to fetch the most latest 10 records.

I tried:

Messages.objects.filter(since=since)[:-10]

And I had an error saying Negative Indexing is not supported.

My current work around is sort ID descending order, and then run:

Messages.objects.filter(since=since)[:10]

But this requires the front end to reverse the order again.

My question is, is there a elegant way to do it?

django
6 Answers

I wanted to retrieve the last 25 messages and solved this problem in the following way

#models.py

class Meta:
        ordering = ['created']

#views.py

message1 = []
    for message in pm_messages.objects.filter(room=room_name).reverse()[0:25]:
        message1.append(message)
    messagess = message1.reverse()
user_166820910

In response to ron_g's comment in Omid Raha's answer:

Consider the case where there are less than 10 records in the list:

Note that this approach

list[:10:-1]

will return an empty list, in contrast to

list[:10][::-1]

which will return all the records in the list, if the total records are less than 10.

user_110460130

you can convert the queryset to a list and select the last n elements normally

messages = list(Messages.objects.filter(since=since))
messages = oldMessageis[-n:len(oldMessageis)]
user_103752080
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