They aren’t saying to not use has_many. They’re saying to not use the association method that gets put on the AR object from has_many. For example, if a User has_many Posts, they’re saying to avoid calling user.posts.

That may seem weird, but the association still has value: for querying. You can still write: User.joins(:posts) for example.

The problem with the association methods is that they aren’t really methods because they always execute a query. A lot of longtime Rails developers get tired of the database being involved in every step of the way in a request, because it leads to a lack of separation of concerns.

Unfortunately I don't. I work less and less on the CRUD part of the apps, however as I recommended in another comment, Phoenix (Elixir's alternative to Rails) does that correctly: associations are used for the purpose of querying, not as methods. In combination with isolated validations and the data gateway isolated, it's easy to achieve separation of concerns and have a more maintainable code-base.