Django QuerySet aggregate based on field value

Question

My model is as follows:

class AssetIdentifications(models.Model):  
    id = models.BigIntegerField(primary_key=True, db_index=True, editable=False, null=False)
    entity = models.ForeignKey(
        "Entity", db_constraint=False, null=False,
    )
    asset = models.ForeignKey(
        "Asset", db_constraint=False, null=False
    )
    type = models.CharField(
        max_length=32,
        null=False,
    )
    vendor = models.CharField(
        max_length=64, null=False
    )
    software = models.CharField(
        max_length=64, null=False
    )
    version = models.CharField(
        max_length=64, null=False
    )

I want to get a queryset that is grouped based on unique values of vendor. The result should look something like this:

{"vendor1": [\<list of AssetIdentifications\>], "vendor2": [\<list of AssetIdentifications\>] ...}

Is this possible with a group_by or aggregate function (I haven't found something like this in the docs)? Or would I have to iterate through the queryset I obtain just through filtering like AssetIdentifications.objects.filter(entity=e)

If you use a ForeignKey toa Vendor model, then this is a lot easier. — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Jul 29, 2020 at 19:18
unfortunately there is no Vendor model, the data for this table does not come from django — AJwr
– AJwr, Commented Jul 29, 2020 at 19:19

willeM_ Van Onsem · Accepted Answer · 2020-07-29 19:26:11Z

1

You can use the groupby(…) function of the itertools module:

from itertools import groupby
from operator import attrgetter

result = {
    k: list(vs)
    for k, vs in
    groupby(AssetIdentifications.objects.order_by('vendor'), attrgetter('vendor'))
}

Here result is a dictionary that maps the vendors on a list of AssetIndentification objects.

answered Jul 29, 2020 at 19:26

willeM_ Van Onsem

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