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?
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"
By "more efficient", I assume you mean you want to avoid hit database multiple times. In that case, you should query once, and then loop through it yourself, also use QuerySet to sort is better than reverse()
my_datapoint = Datapoint.objects.filter(timestamp_lte = max_desired_time).order_by('-timestamp')
def getLatest(desired_time):
for item in my_datapoint:
if item.timestamp <= desired_time:
return item
If you just want simpler syntax, use chain as jdi suggested.
