Count number of records by date in Django
I have a model similar to the following:
class Review(models.Model):
venue = models.ForeignKey(Venue, db_index=True)
review = models.TextField()
datetime_created = models.DateTimeField(default=datetime.now)
I'd like to query the database to get the total number of reviews for a venue grouped by day. The MySQL query would be:
SELECT DATE(datetime_created), count(id)
FROM REVIEW
WHERE venue_id = 2
GROUP BY DATE(datetime_created);
What is the best way to accomplish this in Django? I could just use
Review.objects.filter(venue__pk=2)
and parse the results in the view, but that doesn't seem right to m开发者_如何学编程e.
This should work (using the same MySQL specific function you used):
Review.objects.filter(venue__pk=2)
.extra({'date_created' : "date(datetime_created)"})
.values('date_created')
.annotate(created_count=Count('id'))
Now that Extra()
is being depreciated a more appropriate answer would use Trunc such as this accepted answer
Now the OP's question would be answered as follows
from django.db.models.functions import TruncDay
Review.objects.all()
.annotate(date=TruncDay('datetime_created'))
.values("date")
.annotate(created_count=Count('id'))
.order_by("-date")
Just for completeness, since extra() is aimed for deprecation, one could use this approach:
from django.db.models.expressions import DateTime
Review.objects.all().\
annotate(month=DateTime("timestamp", "month", pytz.timezone("Etc/UTC"))).\
values("month").\
annotate(created_count=Count('id')).\
order_by("-month")
It worked for me in django 1.8, both in sqlite and MySql databases.
If you were storing a date field, you could use this:
from django.db.models import Count
Review.objects.filter(venue__pk = 2)
.values('date').annotate(event_count = Count('id'))
Because you're storing datetime, it's a little more complicated, but this should offer a good starting point. Check out the aggregation docs here.
Also you can define custom function:
from django.db.models.expressions import Func
# create custom sql function
class ExtractDateFunction(Func):
function = "DATE" # thats the name of function, the way it mapped to sql
# pass this function to annotate
Review.objects.filter(venue__pk=2)
.annotate(date_created=ExtractDateFunction("datetime_created"))
.values('date_created')
.annotate(created_count=Count('id'))
Just make sure that your DB engine supports DATE function
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