self_url from Meta with <attribute.id> raises error

[ttecles]

Hi all,

Why am I not able to refer an attribute from a relationship in the self_url for a specific schema but I can in a Relationship.

from marshmallow_jsonapi import Schema, fields

class User:
    def __init__(self, id, name):
        self.id = id
        self.name = name
class Comment:
    def __init__(self, id, body, author):
        self.id = id
        self.body = body
        self.author = author
class Post:
    def __init__(self, id, title, author, comments=None):
        self.id = id
        self.title = title
        self.author = author    # User object
        self.comments = [] if comments is None else comments    # Comment objects


class PostSchema(Schema):
    id = fields.Str(dump_only=True)
    title = fields.Str()
    author = fields.Relationship(
        self_url='/posts/{post_id}/relationships/author',
        self_url_kwargs={'post_id': '<id>'},
        related_url='/authors/{author_id}',
        related_url_kwargs={'author_id': '<author.id>'},
        include_resource_linkage=True,
        type_='users'
    )

    class Meta:
        type_ = 'posts'
        strict = True
        self_url = '/author/{author_id}/posts/{id}/'
        self_url_kwargs = {'id': '<id>', 'author_id': '<author.id>'}
        self_url_many = '/posts/'


class UserSchema(Schema):
    id = fields.Str(dump_only=True)
    name = fields.Str()

    class Meta:
        type_ = 'users'
        strict = True

user = User(id='94', name='Laura')
post = Post(id='1', title='Django is Omakase', author=user)
PostSchema().dump(post)

Here is my example where PostSchema has self_url = '/author/{author_id}/posts/{id}/' and it raises the error below. This is not happening when I specify related_url='/authors/{author_id}' on the relationship

Traceback (most recent call last):
  File "C:/Users/Joan/.PyCharmCE2019.1/config/scratches/scratch_6.py", line 50, in <module>
    PostSchema().dump(post)
  File "D:\Users\Joan\venvs\kii\lib\site-packages\marshmallow\schema.py", line 544, in dump
    original_data=obj)
  File "D:\Users\Joan\venvs\kii\lib\site-packages\marshmallow\schema.py", line 875, in _invoke_dump_processors
    data=data, many=many, original_data=original_data)
  File "D:\Users\Joan\venvs\kii\lib\site-packages\marshmallow\schema.py", line 976, in _invoke_processors
    data = utils.if_none(processor(data, many), data)
  File "D:\Users\Joan\venvs\kii\lib\site-packages\marshmallow_jsonapi\schema.py", line 128, in format_json_api_response
    ret = self.format_items(data, many)
  File "D:\Users\Joan\venvs\kii\lib\site-packages\marshmallow_jsonapi\schema.py", line 389, in format_items
    return self.format_item(data)
  File "D:\Users\Joan\venvs\kii\lib\site-packages\marshmallow_jsonapi\schema.py", line 376, in format_item
    links = self.get_resource_links(item)
  File "D:\Users\Joan\venvs\kii\lib\site-packages\marshmallow_jsonapi\schema.py", line 408, in get_resource_links
    kwargs = resolve_params(item, self.opts.self_url_kwargs or {})
  File "D:\Users\Joan\venvs\kii\lib\site-packages\marshmallow_jsonapi\utils.py", line 52, in resolve_params
    'attribute of {obj!r}'.format(attr_name=attr_name, obj=obj),
AttributeError: 'author.id' is not a valid attribute of {'id': '1', 'author': {'links': {'self': '/posts/1/relationships/author', 'related': '/authors/94'}, 'data': {'type': 'users', 'id': '94'}}, 'title': 'Django is Omakase'}

Thank you for your time.