From 7de83e8bb1e56be47fd387d82bbc86c55325855e Mon Sep 17 00:00:00 2001
From: Zach Daniel <zach@zachdaniel.dev>
Date: Tue, 16 May 2023 14:59:47 -0400
Subject: [PATCH] improvement: add `get_and_lock/1` builtin change

---
 lib/ash/resource/change/builtins.ex     | 16 ++++++++++++++
 lib/ash/resource/change/get_and_lock.ex | 28 +++++++++++++++++++++++++
 2 files changed, 44 insertions(+)
 create mode 100644 lib/ash/resource/change/get_and_lock.ex

diff --git a/lib/ash/resource/change/builtins.ex b/lib/ash/resource/change/builtins.ex
index 1758218e..189ebd22 100644
--- a/lib/ash/resource/change/builtins.ex
+++ b/lib/ash/resource/change/builtins.ex
@@ -107,6 +107,22 @@ defmodule Ash.Resource.Change.Builtins do
     {Ash.Resource.Change.GetAndLockForUpdate, []}
   end
 
+  @doc """
+  Re-fetches the record being updated and locks it for update.
+
+  Only usable with data layers that support locking `:for_update`.
+
+  This happens in a `before_action` hook (so that it is done as part of the transaction).
+
+  If your resource has global validations (in the top level `validations` block), you may
+  want to add `delay_global_validations? true` to your action to ensure they happen on the
+  locked record.
+  """
+  @spec get_and_lock(lock :: Ash.DataLayer.lock_type()) :: Ash.Resource.Change.ref()
+  def get_and_lock(lock) do
+    {Ash.Resource.Change.GetAndLock, [lock: lock]}
+  end
+
   @doc """
   Sets the attribute to the value provided.
 
diff --git a/lib/ash/resource/change/get_and_lock.ex b/lib/ash/resource/change/get_and_lock.ex
new file mode 100644
index 00000000..e8ba2c03
--- /dev/null
+++ b/lib/ash/resource/change/get_and_lock.ex
@@ -0,0 +1,28 @@
+defmodule Ash.Resource.Change.GetAndLock do
+  @moduledoc """
+  Refetches the record being updated or destroyed, and locks it with the given type.
+  """
+  use Ash.Resource.Change
+
+  def change(changeset, opts, context) do
+    Ash.Changeset.before_action(changeset, fn changeset ->
+      primary_key = Ash.Resource.Info.primary_key(changeset.resource)
+      pkey_values = changeset.data |> Map.take(primary_key) |> Map.to_list()
+
+      case changeset.api.get(
+             changeset.resource,
+             pkey_values,
+             tracer: context[:tracer],
+             tenant: context[:tenant],
+             authorize?: false,
+             lock: opts[:lock]
+           ) do
+        {:ok, record} ->
+          %{changeset | data: record}
+
+        {:error, error} ->
+          Ash.Changeset.add_error(changeset, error)
+      end
+    end)
+  end
+end