Follow up: Count of Group Elements With Joins in Django

问题

In order to build on this question here, we encountered another problem regarding aggregate annotations in the Django ORM.

Because we need a join within our query it leads to this clumsy "extra" statement:

Entry.objects.all()
             .extra(select={'week_year': "TO_CHAR(entry_addition.date, 'IW/YYYY')"}, where=["addition_id=entry_addition.id"], tables=['entry_addition'])
             .values('week_year')
             .annotate(Count('addition'))

We created those the following two classes to get rid of the "extra" statement.

class ToChar(Aggregate):
    name = 'ToChar_pg'

    WEEK_YEAR = 'IW/YYYY'

    def __init__(self, lookup, format_, **extra):
        extra['format_'] = format_
        super(ToChar, self).__init__(lookup, **extra)
django.db.models.ToChar = ToChar


class ToChar_pg(django.db.models.sql.aggregates.Aggregate):

    sql_function = 'TO_CHAR'
    sql_template = """%(function)s(%(field)s, '%(format)s')"""

    def __init__(self, col, format_=None, source=None, distinct=False, **extra):
        extra['format'] = format_
        super(ToChar_pg, self).__init__(col, source=source, distinct=distinct, **extra)
django.db.models.ToChar_pg = ToChar_pg

So now, we got this ORM expression:

Entry.objects.all()
             .annotate(week_year=ToChar('addition__date', ToChar.WEEK_YEAR))
             .values('week_year')
             .annotate(count=Count('addition'))

That is the desired SQL statement:

SELECT TO_CHAR("entry_addition"."date", 'IW/YYYY') AS "week_year", COUNT("entry"."addition_id") AS "count"
FROM "entry" LEFT OUTER JOIN "entry_addition" ON ("entry"."addition_id" = "entry_addition"."id")
GROUP BY week_year

That is the actual output:

SELECT TO_CHAR("entry_addition"."date", 'IW/YYYY') AS "week_year", COUNT("entry"."addition_id") AS "count"
FROM "entry" LEFT OUTER JOIN "entry_addition" ON ("entry"."addition_id" = "entry_addition"."id")

Now, the following question arises: where is the "GROUP BY" clause?

来源：https://stackoverflow.com/questions/25081183/follow-up-count-of-group-elements-with-joins-in-django

标签

sql

django

join

orm

annotate