How to use URL placeholders in action?

You should be able to do that by including an article_id in the route params for your post.

# include at top level
post Post, :create, route: "/articles/:article_id/comments"

Your post pointed out to me that being able to nest base_routes could clean this up greatly, so I’m pushing a release w/ that ability soon. Then it would look like this:

defmodule Account.Blog do
  use Ash.Domain,
    extensions: [AshJsonApi.Domain]

  alias Account.Blog.{Article, Comment}

  resources do
    resource Article
    resource Comment
  end

  json_api do
    routes do
      base_route "/articles", Article do
        get(:read)
        post(:article)

        base_route "/:article_id", Comment do
          post :comment # would call the `:comment` create action on comment
        end
      end

      base_route "/comments", Comment do
        get(:read)
        post(:comment)
      end
    end
  end
end

wow @zachdaniel that’s super fast! You comment here is 18hours ago and I see this commit implementing this feature17hrs ago! improvement: support nested `base_route`s · ash-project/ash_json_api@bf77d4d · GitHub

This is something I was also looking for as well. However, I would like to understand the difference between using related or post_to_relationship macro inside the routes vs what you have proposed as a new solution here:

For eg., can the following do the same as what you have proposed as nested base_route for creating comment?

  json_api do
    routes do
      base_route "/articles", Article do
         post_to_relationship :comments
      end
end

@zachdaniel Thank you so much for the quick reply . Updated to the newer version and applied the solution.

related is a route for reading the records of a relationship, i.e

/posts/:id/comments

It can be thought of as an index route that only returns the related records.

post_to_relationship is for “linking” a record or records to another via a relationship. It accepts a very specific input (something called “linkage”), and is typically only used to connect existing things together.

You can see more here: JSON:API — Latest Specification (v1.1)

Just to clarify, please check if my understanding is correct:

1. related option on routes

Use this only for GET requests for related records. Doesn’t work for any other methods.

If Article resource has many Tag relationship, this related option is used to fetch only the associated tags of a specific article.

In this case, the Ash action for the api is placed in the Article resource.

2. post_to_relationship option on routes

Use this option for any other methods other than GET for related records. The related record must already exist. In the case of Article and Tag relationships, both the records must exist already. post_to_relationship is used to create the linkage in ArticleTags resource.

The same applies for patch_relationship, delete_from_relationship to update or delete the link ArticleTags resource record.

In this case, the Ash action for the api is placed in the Article resource.

3. Nested base_route as explained in this post by @zachdaniel

Use this option to do any of the above actions with the main differences as below:

1. Ash action for the nested route is present in the nested resource rather than in the parent resource as in the above options. i.e., GET /articles/:id/tags will be responded by an action in the Tag resource.
2. In the nested resource, one has to take care of creating/updating/deleting all the links manually.

Is my understanding correct?

Yep! Looks right to me