View Source Defining Idiomatic Actions
The best practice is typically to try to push things as far down into your resources as possible.
If you were doing a twitter front page, you might have a tweet resource with a simple action like this:
# use a simple primary read defaults [:read, ...]
And in doing that, you could get all the tweets with something like this:
Tweet |> Ash.Query.for_read(:read) |> Ash.Query.sort(posted_at: :desc) |> Ash.Query.filter(author.id == ^current_user.id or exists(author.friends, id == ^current_user.id)) # assuming the name of your api was `Tweets` |> Tweets.read!()
And that works and in some cases might be the right way to do what you're trying to do And lets say there was a sort drop down that made it sort by popular instead of recent, you could do something like this:
Tweet |> Ash.Query.for_read(:read) |> then(fn query -> case sort do :recent -> Ash.Query.sort(query, posted_at: :desc) :popular -> Ash.Query.sort(query, like_count: :desc) end end) |> Ash.Query.filter(author.id == ^current_user.id or exists(author.friends, id == ^current_user.id)) # assuming the name of your api was `Tweets` |> Tweets.read!()
But the better way to model this would be something like this:
code_interface do define_for MyApp.Tweets define :front_page, args: [:sort_by] end read :front_page do argument :sort_by, :atom do constraints one_of: [:recent, :popular] end prepare MyApp.Tweets.Tweet.Preparations.SortFrontPage filter expr(author.id == ^actor(:id) or exists(author.friends, id == ^actor(:id)) end
Custom preparations allow you to do all sorts of things, in this case handle custom sorting
defmodule MyApp.Tweets.Tweet.Preparations.SortFrontPage do use Ash.Resource.Preparation def prepare(query, _, _) do # We use `prepend?` to put the sort ahead of any other specified sort on the query case Ash.Changeset.get_argument(query, :sort_by) do :recent -> Ash.Query.sort(query, [posted_at: :desc], prepend?: true) :popular -> Ash.Query.sort(query, [like_count: :desc], prepend?: true) end end end
And then you can get the front page of tweets far more cleanly:
If you were using AshGraphql, you could do something like this:
graphql do type :tweet queries do query :front_page, :front_page end end
And because you've made the action encompass the entire logic of fetching the front page, you've got automatic support for API access to your system. This is just one example of the benefits of having idiomatic and complete actions.