Question

In my application I do the following lookup:

my_datapoint = Datapoint.objects.filter(timestamp_lte = desired_time).reverse()[0]

I have to do this several times, for records that are not adjacent in time.

Is there a way to make this more efficient than having several separate QuerySets? Can I combine them?

Answer 1

This has been asked a ton of times on here. You can use chain

from itertools import chain

combined = chain(qs1, qs2, ...)
for item in combined:
    # foo

One alternative to completely separate queryset objects, is to see if you can do it with “OR” queries using the Q objects:
https://docs.djangoproject.com/en/1.4/topics/db/queries/#complex-lookups-with-q-objects

Example from the docs

Poll.objects.get(
    Q(question__startswith='Who'),
    Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6))
)

This example says “objects that have a question starting with ‘Who’, AND, objects with either this pub date OR that pub date”