Django Postgresql ArrayField aggregation

Question

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

Answer 1

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()