# Django 2.2.9.dev20191202104323 文档

# django.contrib.postgres.aggregates.general 源代码

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

    from .mixins import OrderableAggMixin

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

    class ArrayAgg(OrderableAggMixin, Aggregate):
        function = 'ARRAY_AGG'
        template = '%(function)s(%(distinct)s%(expressions)s %(ordering)s)'
        allow_distinct = True

        @property
        def output_field(self):
            return ArrayField(self.source_expressions[0].output_field)

        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(OrderableAggMixin, Aggregate):
        function = 'STRING_AGG'
        template = "%(function)s(%(distinct)s%(expressions)s, '%(delimiter)s'%(ordering)s)"
        allow_distinct = True

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

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