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import django

from django.contrib.postgres.fields import jsonb

try:

    from django.contrib.postgres.fields.jsonb import KeyTransform, KeyTransformTextLookupMixin

except ImportError:

    # backport from Django 2.x

    class KeyTransform(Transform):

        operator = '->'

        nested_operator = '#>'

        def __init__(self, key_name, *args, **kwargs):

            super(KeyTransform, self).__init__(*args, **kwargs)

            self.key_name = key_name

        def as_sql(self, compiler, connection):

            key_transforms = [self.key_name]

            previous = self.lhs

            while isinstance(previous, KeyTransform):

                key_transforms.insert(0, previous.key_name)

                previous = previous.lhs

            lhs, params = compiler.compile(previous)

            if len(key_transforms) > 1:

                return "(%s %s %%s)" % (lhs, self.nested_operator), [key_transforms] + params

            try:

                int(self.key_name)

            except ValueError:

                lookup = "'%s'" % self.key_name

            else:

                lookup = "%s" % self.key_name

            return "(%s %s %s)" % (lhs, self.operator, lookup), params

    jsonb.KeyTransform = KeyTransform

    class KeyTextTransform(KeyTransform):

        operator = '->>'

        nested_operator = '#>>'

        _output_field = TextField()

    class KeyTransformTextLookupMixin(object):

        """

        Mixin for combining with a lookup expecting a text lhs from a JSONField

        key lookup. Make use of the ->> operator instead of casting key values to

        text and performing the lookup on the resulting representation.

        """

        def __init__(self, key_transform, *args, **kwargs):

            assert isinstance(key_transform, KeyTransform)

            key_text_transform = KeyTextTransform(

                key_transform.key_name, *key_transform.source_expressions, **key_transform.extra

            )

            super(KeyTransformTextLookupMixin, self).__init__(key_text_transform, *args, **kwargs)