fix: we cannot assume that after_action/1 can be done atomically

The reason for this is that a given change may access `changeset.data`
which will not be available. This may introduce compile errors for some users
unfortunately, there is nothing we can do about this. They will need to change
to writing custom changes w/ the `atomic/3` callback that adds an after action
hook

improvement: honor a `_union_type` type param when casting unions

documentation/dsls/DSL:-Ash.Resource.md

@@ -1739,7 +1739,7 @@ Declares a `destroy` action. For calling this action, see the `Ash.Domain` docum
 
 ### Examples
 ```
-destroy :soft_delete do
+destroy :destroy do
   primary? true
 end
 

lib/ash/resource/change/after_action.ex

@@ -14,8 +14,10 @@ defmodule Ash.Resource.Change.AfterAction do
     )
   end
 
-  @impl true
+  # we had to remove this. We can't be sure that the change function won't access
-  def atomic(changeset, opts, context) do
+  # `changeset.data`, so cannot do this automatically
-    {:ok, change(changeset, opts, context)}
+  # @impl true
-  end
+  # def atomic(changeset, opts, context) do
+  #   {:ok, change(changeset, opts, context)}
+  # end
 end

lib/ash/resource/dsl.ex

@@ -679,7 +679,7 @@ defmodule Ash.Resource.Dsl do
     """,
     examples: [
       """
-      destroy :soft_delete do
+      destroy :destroy do
         primary? true
       end
       """

lib/ash/type/union.ex

@@ -406,6 +406,18 @@ defmodule Ash.Type.Union do
     end
   end
 
+  def cast_input(%{"_union_type" => union_type} = value, constraints) do
+    case Enum.find(constraints[:types], fn {key, _} ->
+           to_string(key) == union_type
+         end) do
+      {type, _config} ->
+        cast_input(%Ash.Union{value: Map.delete(value, "_union_type"), type: type}, constraints)
+
+      _ ->
+        cast_input(Map.delete(value, "_union_type"), constraints)
+    end
+  end
+
   def cast_input(value, constraints) do
     types = constraints[:types] || []
 

test/actions/bulk/bulk_create_test.exs

@@ -60,6 +60,21 @@ defmodule Ash.Test.Actions.BulkCreateTest do
     end
   end
 
+  defmodule ChangeTitleBeforeAction do
+    use Ash.Resource.Change
+
+    @impl Ash.Resource.Change
+    def change(changeset, _opts, _context) do
+      Ash.Changeset.before_action(changeset, fn changeset ->
+        Ash.Changeset.force_change_attribute(
+          changeset,
+          :title,
+          "before_" <> Ash.Changeset.get_attribute(changeset, :title)
+        )
+      end)
+    end
+  end
+
   defmodule ChangeMessage do
     use Ash.Resource.Change
 
@@ -206,6 +221,11 @@ defmodule Ash.Test.Actions.BulkCreateTest do
       default_accept :*
       defaults [:read, :destroy, create: :*, update: :*]
 
+      create :create_with_before_action do
+        accept [:title]
+        change ChangeTitleBeforeAction
+      end
+
       create :create_with_related_posts do
         argument :related_post_ids, {:array, :uuid} do
           allow_nil? false
@@ -547,6 +567,25 @@ defmodule Ash.Test.Actions.BulkCreateTest do
              )
   end
 
+  test "runs before action hooks" do
+    org =
+      Org
+      |> Ash.Changeset.for_create(:create, %{})
+      |> Ash.create!()
+
+    assert %Ash.BulkResult{records: [%{title: "before_title1"}, %{title: "before_title2"}]} =
+             Ash.bulk_create!(
+               [%{title: "title1"}, %{title: "title2"}],
+               Post,
+               :create_with_before_action,
+               return_records?: true,
+               return_errors?: true,
+               authorize?: false,
+               sorted?: true,
+               tenant: org.id
+             )
+  end
+
   test "runs changes" do
     org =
       Org