CODEWITHSUNDEEP
pythondjangodjango-modelsdjango-ormpython-dateutil
Jagrut Trivedi
Jagrut Trivedi

Reputation: 1319

how to add days to django annotate date field from already built annotation

my model looks like this

class Model(models.Model):
    user_id = models.ForeignKey()
    date = models.DateField()
    field1 = models.FloatField()
    field2 = models.FloatField()

I have a below queryset

queryset = Model.objects.filter(user_id__exact=5) \
                       .annotate(weekstartdate=Trunc('date', 'week')) \
                       .values('weekstartdate') \
                       .annotate(avg_field1=Avg('field1')) \
                       .annotate(avg_field2=Avg('field2')) \
                       .order_by('-weekstartdate')

which is working perfectly. now I want to add weekenddate field to above queryset which has a date = weekstartdate + 6 days. I have added below line to above query

.annotate(weekenddate=Trunc('date', 'week') + timedelta(days=7), output_field=DateField())

but it is complaining :-

TypeError: QuerySet.annotate() received non-expression(s): <django.db.models.fields.DateField>

Relative imports

from django.db.models import Avg, Q
from django.db.models.functions import Trunc
from django.db.models import DateTimeField, ExpressionWrapper, F, DateField

Note :- Simple for loop after queryset is not i am looking for because after assigning manually a field, queryset filter is still fetching query from old queryset due to laziness of the queryset. If answer can be in relativedelta of dateutil library it would be much better.

Upvotes: 0

Views: 3455

Answers (1)

Nafees Anwar
Nafees Anwar

Reputation: 6608

You need to use ExpressionWrapper around it.

YourModel.objects.annotate(
    weekenddate=models.ExpressionWrapper(
        Trunc('date', 'week') + timedelta(days=7),
        output_field=models.DateField(),
    ),
)

Upvotes: 1

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