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djangopostgresqldjango-querysetaggregation
elynch
elynch

Reputation: 2240

Django Postgresql ArrayField aggregation

In my Django application, using Postgresql, I have a model with an ArrayField of CharFields. I would like to know if there's a DB way to aggregate and get a list of all the strings in the table. For example:

  1. ['dog', 'cat']
  2. ['dog']
  3. ['cat']

would yield ['dog', 'cat']

I know how to do that in Python but would like to find out a way to aggregate this on the DB level. Using Django 1.8.4

Upvotes: 24

Views: 9853

Answers (1)

Ivan
Ivan

Reputation: 6013

In PostgreSQL you can do the following:

SELECT DISTINCT UNNEST(array_column) FROM the_table;

So if your model looks something like

class TheModel(models.Model):
    # ...
    array_field = ArrayField(models.CharField(max_length=255, blank=True),\
                             default=list)
    # ...

the Django equivalent is:

from django.db.models import Func, F
TheModel.objects.annotate(arr_els=Func(F('array_field'), function='unnest'))\
                .values_list('arr_els', flat=True).distinct()

Upvotes: 50

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