# documentação Django 2.0.8

# Código fonte para django.contrib.postgres.fields.jsonb

    import json

    from psycopg2.extras import Json

    from django.contrib.postgres import forms, lookups
    from django.core import exceptions
    from django.db.models import (
        Field, TextField, Transform, lookups as builtin_lookups,
    )
    from django.utils.translation import gettext_lazy as _

    __all__ = ['JSONField']

    class JsonAdapter(Json):
        """
        Customized psycopg2.extras.Json to allow for a custom encoder.
        """
        def __init__(self, adapted, dumps=None, encoder=None):
            self.encoder = encoder
            super().__init__(adapted, dumps=dumps)

        def dumps(self, obj):
            options = {'cls': self.encoder} if self.encoder else {}
            return json.dumps(obj, **options)

    class JSONField(Field):
        empty_strings_allowed = False
        description = _('A JSON object')
        default_error_messages = {
            'invalid': _("Value must be valid JSON."),
        }

        def __init__(self, verbose_name=None, name=None, encoder=None, **kwargs):
            if encoder and not callable(encoder):
                raise ValueError("The encoder parameter must be a callable object.")
            self.encoder = encoder
            super().__init__(verbose_name, name, **kwargs)

        def db_type(self, connection):
            return 'jsonb'

        def deconstruct(self):
            name, path, args, kwargs = super().deconstruct()
            if self.encoder is not None:
                kwargs['encoder'] = self.encoder
            return name, path, args, kwargs

        def get_transform(self, name):
            transform = super().get_transform(name)
            if transform:
                return transform
            return KeyTransformFactory(name)

        def get_prep_value(self, value):
            if value is not None:
                return JsonAdapter(value, encoder=self.encoder)
            return value

        def validate(self, value, model_instance):
            super().validate(value, model_instance)
            options = {'cls': self.encoder} if self.encoder else {}
            try:
                json.dumps(value, **options)
            except TypeError:
                raise exceptions.ValidationError(
                    self.error_messages['invalid'],
                    code='invalid',
                    params={'value': value},
                )

        def value_to_string(self, obj):
            return self.value_from_object(obj)

        def formfield(self, **kwargs):
            defaults = {'form_class': forms.JSONField}
            defaults.update(kwargs)
            return super().formfield(**defaults)

    JSONField.register_lookup(lookups.DataContains)
    JSONField.register_lookup(lookups.ContainedBy)
    JSONField.register_lookup(lookups.HasKey)
    JSONField.register_lookup(lookups.HasKeys)
    JSONField.register_lookup(lookups.HasAnyKeys)

    class KeyTransform(Transform):
        operator = '->'
        nested_operator = '#>'

        def __init__(self, key_name, *args, **kwargs):
            super().__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

    class KeyTextTransform(KeyTransform):
        operator = '->>'
        nested_operator = '#>>'
        output_field = TextField()

    class KeyTransformTextLookupMixin:
        """
        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().__init__(key_text_transform, *args, **kwargs)

    class KeyTransformIExact(KeyTransformTextLookupMixin, builtin_lookups.IExact):
        pass

    class KeyTransformIContains(KeyTransformTextLookupMixin, builtin_lookups.IContains):
        pass

    class KeyTransformStartsWith(KeyTransformTextLookupMixin, builtin_lookups.StartsWith):
        pass

    class KeyTransformIStartsWith(KeyTransformTextLookupMixin, builtin_lookups.IStartsWith):
        pass

    class KeyTransformEndsWith(KeyTransformTextLookupMixin, builtin_lookups.EndsWith):
        pass

    class KeyTransformIEndsWith(KeyTransformTextLookupMixin, builtin_lookups.IEndsWith):
        pass

    class KeyTransformRegex(KeyTransformTextLookupMixin, builtin_lookups.Regex):
        pass

    class KeyTransformIRegex(KeyTransformTextLookupMixin, builtin_lookups.IRegex):
        pass

    KeyTransform.register_lookup(KeyTransformIExact)
    KeyTransform.register_lookup(KeyTransformIContains)
    KeyTransform.register_lookup(KeyTransformStartsWith)
    KeyTransform.register_lookup(KeyTransformIStartsWith)
    KeyTransform.register_lookup(KeyTransformEndsWith)
    KeyTransform.register_lookup(KeyTransformIEndsWith)
    KeyTransform.register_lookup(KeyTransformRegex)
    KeyTransform.register_lookup(KeyTransformIRegex)

    class KeyTransformFactory:

        def __init__(self, key_name):
            self.key_name = key_name

        def __call__(self, *args, **kwargs):
            return KeyTransform(self.key_name, *args, **kwargs)