From b81ed99571957e9fed43dab764f7bff209cc0dea Mon Sep 17 00:00:00 2001
From: Moritz <moritz.m@local-it.org>
Date: Mon, 15 Dec 2025 12:32:05 +0100
Subject: [PATCH] fix: prevent deadlocks by detecting existing transactions

---
 lib/membership/member.ex                  |  2 +-
 lib/mv/membership_fees/cycle_generator.ex | 69 +++++++++++++++--------
 2 files changed, 46 insertions(+), 25 deletions(-)

diff --git a/lib/membership/member.ex b/lib/membership/member.ex
index 5862a25..8e67570 100644
--- a/lib/membership/member.ex
+++ b/lib/membership/member.ex
@@ -763,7 +763,7 @@ defmodule Mv.Membership.Member do
   end
 
   # Regenerates cycles with new type/amount
-  # CycleGenerator uses its own transaction with advisory lock
+  # CycleGenerator detects if already in transaction and uses advisory lock accordingly
   defp regenerate_cycles(member_id) do
     case Mv.MembershipFees.CycleGenerator.generate_cycles_for_member(member_id) do
       {:ok, _cycles} -> :ok
diff --git a/lib/mv/membership_fees/cycle_generator.ex b/lib/mv/membership_fees/cycle_generator.ex
index 0727a62..4ed7ee7 100644
--- a/lib/mv/membership_fees/cycle_generator.ex
+++ b/lib/mv/membership_fees/cycle_generator.ex
@@ -188,36 +188,57 @@ defmodule Mv.MembershipFees.CycleGenerator do
     # Convert UUID to integer for advisory lock (use hash)
     lock_key = :erlang.phash2(member_id)
 
-    result =
-      Repo.transaction(fn ->
-        # Acquire advisory lock for this transaction
-        Ecto.Adapters.SQL.query!(Repo, "SELECT pg_advisory_xact_lock($1)", [lock_key])
+    # Check if we're already in a transaction (e.g., called from Ash action)
+    if Repo.in_transaction?() do
+      # Already in transaction: use advisory lock directly without starting new transaction
+      # This prevents nested transactions which can cause deadlocks
+      Ecto.Adapters.SQL.query!(Repo, "SELECT pg_advisory_xact_lock($1)", [lock_key])
 
-        case fun.() do
-          {:ok, result, notifications} when is_list(notifications) ->
-            # Return result and notifications separately
-            {result, notifications}
+      case fun.() do
+        {:ok, result, notifications} when is_list(notifications) ->
+          # Notifications will be sent after the outer transaction commits
+          # Return in same format as non-transaction case for consistency
+          {:ok, result}
 
-          {:ok, result} ->
-            # Handle case where no notifications were returned (backward compatibility)
-            {result, []}
+        {:ok, result} ->
+          {:ok, result}
 
-          {:error, reason} ->
-            Repo.rollback(reason)
-        end
-      end)
+        {:error, reason} ->
+          {:error, reason}
+      end
+    else
+      # Not in transaction: start new transaction with advisory lock
+      result =
+        Repo.transaction(fn ->
+          # Acquire advisory lock for this transaction
+          Ecto.Adapters.SQL.query!(Repo, "SELECT pg_advisory_xact_lock($1)", [lock_key])
 
-    # Extract result and notifications, send notifications after transaction
-    case result do
-      {:ok, {cycles, notifications}} ->
-        if Enum.any?(notifications) do
-          Ash.Notifier.notify(notifications)
-        end
+          case fun.() do
+            {:ok, result, notifications} when is_list(notifications) ->
+              # Return result and notifications separately
+              {result, notifications}
 
-        {:ok, cycles}
+            {:ok, result} ->
+              # Handle case where no notifications were returned (backward compatibility)
+              {result, []}
 
-      {:error, reason} ->
-        {:error, reason}
+            {:error, reason} ->
+              Repo.rollback(reason)
+          end
+        end)
+
+      # Extract result and notifications, send notifications after transaction
+      case result do
+        {:ok, {cycles, notifications}} ->
+          if Enum.any?(notifications) do
+            Ash.Notifier.notify(notifications)
+          end
+
+          {:ok, cycles}
+
+        {:error, reason} ->
+          {:error, reason}
+      end
     end
   end