from marshmallow_jsonapi import Schema, fields
class PostSchema(Schema):
    id = fields.Str(dump_only=True)
    title = fields.Str()
    author = fields.Relationship(
        "/authors/{author_id}", related_url_kwargs={"author_id": "<author.id>"}
    )
    comments = fields.Relationship(
        "/posts/{post_id}/comments",
        related_url_kwargs={"post_id": "<id>"},
        # Include resource linkage
        many=True,
        include_resource_linkage=True,
        type_="comments",
    )
    class Meta:
        type_ = "posts"
post_schema = PostSchema()
post_schema.dump(post)
# {
#     "data": {
#         "id": "1",
#         "type": "posts"
#         "attributes": {
#             "title": "JSON API paints my bikeshed!"
#         },
#         "relationships": {
#             "author": {
#                 "links": {
#                     "related": "/authors/9"
#                 }
#             },
#             "comments": {
#                 "links": {
#                     "related": "/posts/1/comments/"
#                 }
#                 "data": [
#                     {"id": 5, "type": "comments"},
#                     {"id": 12, "type": "comments"}
#                 ],
#             }
#         },
#     }
# }