ecomonde/ecomonde-venv/lib/python3.4/site-packages/django/contrib/postgres/aggregates/general.py

from django.db.models.aggregates import Aggregate

__all__ = [
    'ArrayAgg', 'BitAnd', 'BitOr', 'BoolAnd', 'BoolOr', 'StringAgg',
]


class ArrayAgg(Aggregate):
    function = 'ARRAY_AGG'

    def convert_value(self, value, expression, connection, context):
        if not value:
            return []
        return value


class BitAnd(Aggregate):
    function = 'BIT_AND'


class BitOr(Aggregate):
    function = 'BIT_OR'


class BoolAnd(Aggregate):
    function = 'BOOL_AND'


class BoolOr(Aggregate):
    function = 'BOOL_OR'


class StringAgg(Aggregate):
    function = 'STRING_AGG'
    template = "%(function)s(%(expressions)s, '%(delimiter)s')"

    def __init__(self, expression, delimiter, **extra):
        super(StringAgg, self).__init__(expression, delimiter=delimiter, **extra)

    def convert_value(self, value, expression, connection, context):
        if not value:
            return ''
        return value