# documentação Django 2.0.8

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

    from django.contrib.postgres.fields import JSONField
    from django.db.models.aggregates import Aggregate

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

    class ArrayAgg(Aggregate):
        function = 'ARRAY_AGG'
        template = '%(function)s(%(distinct)s%(expressions)s)'

        def __init__(self, expression, distinct=False, **extra):
            super().__init__(expression, distinct='DISTINCT ' if distinct else '', **extra)

        def convert_value(self, value, expression, connection):
            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 JSONBAgg(Aggregate):
        function = 'JSONB_AGG'
        output_field = JSONField()

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

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

        def __init__(self, expression, delimiter, distinct=False, **extra):
            distinct = 'DISTINCT ' if distinct else ''
            super().__init__(expression, delimiter=delimiter, distinct=distinct, **extra)

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