# documentación de Django - 1.10.7

# Código fuente para django.contrib.postgres.aggregates.general

    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