Django PostgreSQL string_agg

string_agg.py

#models.py

from django.db.models import Aggregate

class Concat(Aggregate):
    def add_to_query(self, query, alias, col, source, is_summary):
        #we send source=CharField to prevent Django from casting string to int
        aggregate = SQLConcat(col, source=models.CharField(), is_summary=is_summary, **self.extra)
        query.aggregates[alias] = aggregate
    def __init__(self, col, distinct=False, **extra):

        super(Concat, self).__init__(col, distinct=(
                                               distinct and 'DISTINCT ' or ''),
                                          **extra)
#For PostgreSQL >= 9.0
from django.db.models.sql.aggregates import Aggregate as SQLAggregate
#Aways use with separator, e.g. .annotate(values=Concat('value', separator=','))
class SQLConcat(SQLAggregate):
    sql_function = 'string_agg'
    @property
    def sql_template(self):
        #the ::text cast is a hardcoded hack to work with integer columns
        return "%(function)s(%(distinct)s(%(field)s), '%(separator)s')"

#Usage

from app_name.models import Concat

model_name.objects().all().values('field_1').annotate(distinct_concatenation=Concat('some_other_field',separator=',',distinct=True))