improvement: support prefer_transaction? on DataLayer

documentation/dsls/DSL-Ash.Notifier.PubSub.md

@@ -10,6 +10,25 @@ This is plug and play with `Phoenix.PubSub`, but could be used with any pubsub s
 You configure a module that defines a `broadcast/3` function, and then add some "publications"
 which configure under what conditions an event should be sent and what the topic should be.
 
+## Example
+
+```elixir
+defmodule MyApp.User do
+  use Ash.Resource,
+    # ...
+    notifiers: [Ash.Notifier.PubSub]
+
+  # ...
+
+  pub_sub do
+    module MyAppWeb.Endpoint
+
+    prefix "user"
+    publish :update, ["updated", :_pkey]
+  end
+end
+```
+
 ## Debugging PubSub
 
 It can be quite frustrating when setting up pub_sub when everything appears to be set up properly, but

lib/ash/actions/update/bulk.ex

@@ -244,7 +244,11 @@ defmodule Ash.Actions.Update.Bulk do
                 :bulk_destroy
             end
 
-          if (has_after_batch_hooks? || !Enum.empty?(atomic_changeset.after_action)) &&
+          prefer_transaction? =
+            has_after_batch_hooks? || !Enum.empty?(atomic_changeset.after_action) ||
+              Ash.DataLayer.prefer_transaction?(atomic_changeset.resource)
+
+          if prefer_transaction? &&
                Keyword.get(opts, :transaction, true) do
             Ash.DataLayer.transaction(
               List.wrap(atomic_changeset.resource) ++ atomic_changeset.action.touches_resources,

lib/ash/changeset/changeset.ex

@@ -3356,7 +3356,16 @@ defmodule Ash.Changeset do
   end
 
   def with_hooks(changeset, func, opts) do
-    if opts[:transaction?] && Ash.DataLayer.data_layer_can?(changeset.resource, :transact) do
+    prefer_transaction? =
+      if Enum.empty?(changeset.before_action) && Enum.empty?(changeset.after_action) &&
+           Enum.empty?(changeset.around_action) do
+        Ash.DataLayer.prefer_transaction?(changeset.resource)
+      else
+        true
+      end
+
+    if prefer_transaction? && opts[:transaction?] &&
+         Ash.DataLayer.data_layer_can?(changeset.resource, :transact) do
       transaction_hooks(changeset, fn changeset ->
         resources =
           changeset.resource

lib/ash/data_layer/data_layer.ex

@@ -281,6 +281,7 @@ defmodule Ash.DataLayer do
   @callback rollback(Ash.Resource.t(), term) :: no_return
   @callback calculate(Ash.Resource.t(), list(Ash.Expr.t()), context :: map) ::
               {:ok, term} | {:error, term}
+  @callback prefer_transaction?(Ash.Resource.t()) :: boolean
   @callback can?(Ash.Resource.t() | Spark.Dsl.t(), feature()) :: boolean
   @callback set_context(Ash.Resource.t(), data_layer_query(), map) ::
               {:ok, data_layer_query()} | {:error, term}
@@ -297,6 +298,7 @@ defmodule Ash.DataLayer do
                       create: 2,
                       update: 2,
                       set_context: 3,
+                      prefer_transaction?: 1,
                       calculate: 3,
                       destroy: 2,
                       filter: 3,
@@ -357,6 +359,19 @@ defmodule Ash.DataLayer do
     data_layer(resource).calculate(resource, exprs, context)
   end
 
+  @spec prefer_transaction?(Ash.Resource.t()) :: boolean
+  def prefer_transaction?(resource) do
+    data_layer = data_layer(resource)
+
+    if function_exported?(data_layer, :prefer_transaction?, 1) do
+      data_layer.prefer_transaction?(resource)
+    else
+      # default to false in 4.0
+      # also change in postgres data layer to default to false
+      true
+    end
+  end
+
   @doc "Wraps the execution of the function in a transaction with the resource's data_layer"
   @spec transaction(
           Ash.Resource.t() | [Ash.Resource.t()],