feat(ex/detours): add add_author?/2 function and replace with_author

lib/skate/detours/db/detour.ex

@@ -69,6 +69,7 @@ defmodule Skate.Detours.Db.Detour do
       %{virtual_fields: wanted_virtual_fields, fields: wanted_fields} = split_fields(fields)
 
       query
+      |> add_author?(wanted_fields)
       |> select_merge(^wanted_fields)
       |> select_virtual_fields(wanted_virtual_fields)
     end
@@ -106,6 +107,25 @@ defmodule Skate.Detours.Db.Detour do
       order_by(query, desc: :updated_at)
     end
 
+    defp add_author?(query, fields) do
+      if Keyword.has_key?(fields, :author) do
+        with_author(query)
+      else
+        query
+      end
+    end
+
+    @doc """
+    Joins the `Skate.Settings.Db.User` struct into the `Skate.Detours.Db.Detour`
+    via Ecto preload.
+
+    > ### Primary Keys required in query when using `with_author/1` {:.warning}
+    > When preloading structs, Ecto requires that primary key fields are also
+    > queried on all preloaded structs.
+    > This means that when querying `:author` via `select_fields`, you need to
+    > explicitly request `:id` on both the `Skate.Detours.Db.Detour` and the
+    > `Skate.Settings.Db.User`.
+    """
     def with_author(query \\ base()) do
       from([detour: d] in query,
         join: a in assoc(d, :author),

lib/skate/detours/detours.ex

@@ -27,7 +27,6 @@ defmodule Skate.Detours.Detours do
 
   def list_detours(fields) do
     Skate.Detours.Db.Detour.Queries.select_fields(fields)
-    |> Skate.Detours.Db.Detour.Queries.with_author()
     |> Skate.Detours.Db.Detour.Queries.sorted_by_last_updated()
     |> Repo.all()
   end