def save_storage(self, instance, schema):
        """Save basic:json values to a Storage collection."""
        for field_schema, fields in iterate_fields(instance, schema):
            name = field_schema['name']
            value = fields[name]
            if field_schema.get('type', '').startswith('basic:json:'):
                if value and not self.pk:
                    raise ValidationError(
                        'Data object must be `created` before creating `basic:json:` fields')

                if isinstance(value, int):
                    # already in Storage
                    continue

                if isinstance(value, str):
                    file_path = self.location.get_path(filename=value)  # pylint: disable=no-member
                    if os.path.isfile(file_path):
                        try:
                            with open(file_path) as file_handler:
                                value = json.load(file_handler)
                        except json.JSONDecodeError:
                            with open(file_path) as file_handler:
                                content = file_handler.read()
                                content = content.rstrip()
                                raise ValidationError(
                                    "Value of '{}' must be a valid JSON, current: {}".format(name, content)
                                )

                storage = self.storages.create(  # pylint: disable=no-member
                    name='Storage for data id {}'.format(self.pk),
                    contributor=self.contributor,
                    json=value,
                )

                # `value` is copied by value, so `fields[name]` must be changed
                fields[name] = storage.pk