I have this model:
class Person(models.Model):
city = models.CharField(max_length=20, blank=True)
added_date = models.DateField(default=datetime.date.today)
I want to create a template/view that has a table of months and the number of people added that month (ie, 5 in january, 10 in february, 8 in march, etc.). I have a similar table for all the people from a each city using:
cities = Patient.objects.values('city').annotate(city_count=Count('city')).order_by('-city_count')
I don't know how to do that for my months table. I could filter for a particular month, then count all. But then I'd need to run that through a loop over every month, which would be multiple database hits. I don't want to do that.
Is there a way to do this without writing sql and just using django's api?
Its a very old thread, but i guess I'll answer in case someone else ended up here looking for a solution.
The solution is for Django 1.10+ using the ExtractMonth function, for more detail visit official documentation
First you have to import ExtractMonth, like
from django.db.models.functions import ExtractMonth
Then using your Persons model, the code will be like this
personsMonthlyData = Person.objects.annotate(month=ExtractMonth('added_date')).values('month').annotate(count=Count('id')).order_by('month')
personsMonthlyData will output something like this
[{month: 1, count: 3}, {month: 2: count: 1}]
where month represent the month number e.g. 1 for January and 2 for February and the count against each month is assigned to the count item.
I hope this helps.
The fact that most DBs have such a perfect way of doing this with a GROUP BY query that has no analog in Django AFAIK would lead me to drop into SQL to do this. I did a google search for "django sql" and turned up this post by Doug Hellman on this exact problem: http://blog.doughellmann.com/2007/12/using-raw-sql-in-django.html. I would use that as a starting point for getting your month counts into Django.
Related
I have a model Sales with:
Saler
Product sold
Date
I would like to get the first sale for each date and for each saler, how can I do that?
Thanks
Considering the model Posted in the question, the Django ORM query will be:
first_sale = Sales.objects.order_by("Saler", "Date").distinct("Saler")
Not tested, but I would try (I assumed the field for the date of the sale is named sale_date, and is of type Datetime):
first_sale = Sales.objects.filter(saler=the_saler, sale_date__date=datetime.date(2021, 05, 19)).order_by('sale_date').first()
filter will restrict the search to a given saler (the_saler), and to a given day (see the __date expression: https://docs.djangoproject.com/fr/3.1/ref/models/querysets/#date)
order_by and first will give you the first of the day.
My proj has a model that goes like:
class Data(Model):
data = FloatField(verbose_name='Data', null=True, blank=True)
created_at = DateTimeField(verbose_name='Created at')
And my app creates a few hundred logs of this model per day.
I'm trying to sum only the greatest values of each day, without having to iterate over them (using only Django queries).
Is it possible without writing SQL queries?
PS: I'm able to get the greatest 'data' of each day, so the current logic iterates over days and sums the greatest values of each day. But that solution is becoming too slow and I'd like to solve it directly into db level.
Annotations and aggregates to the rescue:
from django.db.models import Sum, Max
from django.db.models.functions import Trunc
report = (Data.objects
.annotate(day=Trunc('created_at', 'day'))
.values('day')
.annotate(greatest=Max('data'))
.values('greatest')
.aggregate(total=Sum('greatest'))
)
print(report['total'])
The resulting SQL is almost simpler than the code:
SELECT SUM("greatest")
FROM
(SELECT MAX("app_data"."data_id") AS "greatest"
FROM "app_data"
GROUP BY DATE_TRUNC('day', "app_data"."created_at")) subquery
If you are using a database backed that supports distinct on fields (like postgres does) you can do.
Data.objects.order_by('created_at__date', '-data').distinct('created_at__date')
I have this model for employee overtime hours
class Overtime(IncomeBase):
day = models.DateField(verbose_name="Date")
value = models.FloatField(default=1)
I need to extract the total value for each month. Now I am using a daily QuerySet in the manager.
class OvertimeManager(models.Manager):
def daily_report(self):
return self.values('day').annotate(hours=models.Sum('value')).order_by('-day')
However now I need a monthly report that will get the Sum of value for each month.
I tried to extract the month first but then I lose the values.
Note: the month should not have the total sum for all years, so specifically I need to group by month,year
If you are using Postgresql you can do this. Ofc there is similar fuctions.
Overtime.objects.extra({'month': "to_char(day, 'Mon')", "year": "extract(year from day)"}).values('month', 'year').annotate(Sum('value'))
More info:
http://www.postgresql.org/docs/7.4/static/functions-formatting.html
http://www.postgresql.org/docs/9.1/static/functions-datetime.html
Or django way:
from django.db import connection
truncate_month = connection.ops.date_trunc_sql('month','day')
Overtime.objects.extra({'month': truncate_month}).values('month').annotate(Sum('value'))
I think this will help you.
I have a model like this:
class MovieHistory(models.Model):
watched_by = models.ForeignKey(User)
time = models.DateTimeField(auto_now_add=True)
movie = models.ForeignKey(Movie)
I want to get up to 15 movies that were watched the most in the last 30 days. So far I have this:
Movie.objects.filter(time__gte=datetime.now()-timedelta(days=30))
How do you filter again, and order them by movie count? I know that I can filter the first 15 results like this: [:15], but I don't know how to order by the amount of movies in that model, and only pick one of each (so I don't have repeated MovieHistories with the same movies on each one).
Thanks.
Annotation is likely the best approach:
from django.db.models import Count
most_watched = Movie.objects.all().annotate(num_watched = Count('watched_by')).order_by('-num_watched')[:15]
I haven't tested this, but I believe this is on the way to the answer. Please let me know if it works! You may need to replace count('watched_by') by Count('watched_by_id') or whatever the field name is in your database (check with ./manage.py sql your_appname).
Hope this helps!
For more on using these annotations: https://docs.djangoproject.com/en/dev/topics/db/aggregation/#cheat-sheet
I'm working with an Article like model that has a DateTimeField(auto_now_add=True) to capture the publication date (pub_date). This looks something like the following:
class Article(models.Model):
text = models.TextField()
pub_date = models.DateTimeField(auto_now_add=True)
I want to do a query that counts how many article posts or entries have been added per day. In other words, I want to query the entries and group them by day (and eventually month, hour, second, etc.). This would look something like the following in the SQLite shell:
select pub_date, count(id) from "myapp_article"
where id = 1
group by strftime("%d", pub_date)
;
Which returns something like:
2012-03-07 18:08:57.456761|5
2012-03-08 18:08:57.456761|9
2012-03-09 18:08:57.456761|1
I can't seem to figure out how to get that result from a Django QuerySet. I am aware of how to get a similar result using itertools.groupby, but that isn't possible in this situation (explanation to follow).
The end result of this query will be used in a graph showing the number of posts per day. I'm attempting to use the Django Chartit package to achieve this goal. Chartit puts a constraint on the data source (DataPool). The source must be a Model, Manager, or QuerySet, so using itertools.groupby is not an option as far as I can tell.
So the question is... How do I group or aggregate the entries by day and end up with a QuerySet object?
Create an extra field that only store date data(not time) and annotate with Count:
Article.objects.extra({'published':"date(pub_date)"}).values('published').annotate(count=Count('id'))
Result will be:
published,count
2012-03-07,5
2012-03-08,9
2012-03-09,1