Django gets error when overriding save method

Question

I overriding model's save() method to do some work with directory.

My overrided save() method looks like this:

def save(self, *args, **kwargs):
    book_dir = os.path.join(MEDIA_ROOT, self.title)

    # check that at least one file is loading
    if all([self.pdf, self.fb2, self.epub]):
        raise ValidationError("At least 1 file should be uploaded!")
    # create book's directory if it not exists
    if os.path.exists(book_dir):
        raise ValidationError("This book is already exists!")
    else:
        os.mkdir(book_dir)

    # assign uploading files storage
    for x in [self.image, self.pdf, self.fb2, self.epub]:
        x.storage = book_dir

    super().save(*args, **kwargs)  # Call the "real" save() method.

Everything goes well until last line. Django gives me AttributeError: 'str' object has no attribute 'save' error.

UPD 1: Added full model

class Book(models.Model):
    title = models.CharField(
        verbose_name="Book title",
        max_length=75,
        null=False,
        unique=True,
        )
    year_pub = models.IntegerField(
        verbose_name="Year published",
        null=False
        )
    image = models.ImageField(
        verbose_name="Preview image",
        null=False
        )
    pdf = models.FileField(
        verbose_name="PDF file",
        null=True,
        blank=True,
        validators=[validators.validate_book_ext]
        )
    fb2 = models.FileField(
        verbose_name="FB2 file",
        null=True,
        blank=True,
        validators=[validators.validate_book_ext]
        )
    epub = models.FileField(
        verbose_name="EPUB file",
        null=True,
        blank=True,
        validators=[validators.validate_book_ext]
        )

    def save(self, *args, **kwargs):
        book_dir = os.path.join(MEDIA_ROOT, self.title)

        # check that at least one file is loading
        if all([self.pdf, self.fb2, self.epub]):
            raise ValidationError("At least 1 file should be uploaded!")
        # create book's directory if it not exists
        if os.path.exists(book_dir):
            raise ValidationError("This book is already exists!")
        else:
            os.mkdir(book_dir)

        # assign uploading files storage
        for x in [self.image, self.pdf, self.fb2, self.epub]:
            x.storage = book_dir

        super().save(*args, **kwargs)  # Call the "real" save() method.

UPD 2: Added traceback

Traceback (most recent call last):
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\core\handlers\exception.py", line 34, in inner
    response = get_response(request)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\core\handlers\base.py", line 115, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\core\handlers\base.py", line 113, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\contrib\admin\options.py", line 606, in wrapper
    return self.admin_site.admin_view(view)(*args, **kwargs)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\utils\decorators.py", line 142, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\views\decorators\cache.py", line 44, in _wrapped_view_func
    response = view_func(request, *args, **kwargs)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\contrib\admin\sites.py", line 223, in inner
    return view(request, *args, **kwargs)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\contrib\admin\options.py", line 1634, in add_view
    return self.changeform_view(request, None, form_url, extra_context)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\utils\decorators.py", line 45, in _wrapper
    return bound_method(*args, **kwargs)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\utils\decorators.py", line 142, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\contrib\admin\options.py", line 1522, in changeform_view
    return self._changeform_view(request, object_id, form_url, extra_context)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\contrib\admin\options.py", line 1561, in _changeform_view
    self.save_model(request, new_object, form, not add)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\contrib\admin\options.py", line 1088, in save_model
    obj.save()
  File "C:\Users\yuyuko\Documents\dev\project3\djangoApp\library\models.py", line 58, in save
    super().save(*args, **kwargs)  # Call the "real" save() method.
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\db\models\base.py", line 741, in save
    force_update=force_update, update_fields=update_fields)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\db\models\base.py", line 779, in save_base
    force_update, using, update_fields,
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\db\models\base.py", line 870, in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\db\models\base.py", line 908, in _do_insert
    using=using, raw=raw)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\db\models\manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\db\models\query.py", line 1186, in _insert
    return query.get_compiler(using=using).execute_sql(return_id)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\db\models\sql\compiler.py", line 1334, in execute_sql
    for sql, params in self.as_sql():
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\db\models\sql\compiler.py", line 1278, in as_sql
    for obj in self.query.objs
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\db\models\sql\compiler.py", line 1278, in <listcomp>
    for obj in self.query.objs
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\db\models\sql\compiler.py", line 1277, in <listcomp>
    [self.prepare_value(field, self.pre_save_val(field, obj)) for field in fields]
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\db\models\sql\compiler.py", line 1228, in pre_save_val
    return field.pre_save(obj, add=True)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\db\models\fields\files.py", line 288, in pre_save
    file.save(file.name, file.file, save=False)
  File "c:\Users\yuyuko\Documents\dev\project3\env\lib\site-packages\django\db\models\fields\files.py", line 87, in save
    self.name = self.storage.save(name, content, max_length=self.field.max_length)
AttributeError: 'str' object has no attribute 'save'
[19/Sep/2019 23:11:03] "POST /admin/library/book/add/ HTTP/1.1" 500 181939

Answer 1

So, i missed 1 more method of storage to override.

Now my overwriting loop storage location works well and looks like this:

# rename and edit storage location of books to book_dir
for field in [self.image, self.pdf, self.fb2, self.epub]:
    field.storage.location = book_dir