From 0e43f89af9dea2e741bbda9b26ab0a087a392fe2 Mon Sep 17 00:00:00 2001
From: Tadhg Boyle <tadhgsmboyle@gmail.com>
Date: Wed, 14 Oct 2026 14:08:09 -0700
Subject: [PATCH] Fix false success for failed unless_exist writes

Use the result of lock_and_write instead of marking a write successful before persistence. Cover handled write failures and avoid populating the local cache with an unpersisted value.
---
 lib/solid_cache/store/api.rb  |  8 ++------
 test/unit/solid_cache_test.rb | 17 +++++++++++++++++
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/lib/solid_cache/store/api.rb b/lib/solid_cache/store/api.rb
index b7859ab0..ecd6c620 100644
--- a/lib/solid_cache/store/api.rb
+++ b/lib/solid_cache/store/api.rb
@@ -53,12 +53,8 @@ def write_entry(key, entry, raw: false, unless_exist: false, **options)
           payload = serialize_entry(entry, raw: raw, **options)
 
           if unless_exist
-            written = false
-            entry_lock_and_write(key) do |value|
-              if value.nil? || deserialize_entry(value, **options).expired?
-                written = true
-                payload
-              end
+            written = !!entry_lock_and_write(key) do |value|
+              payload if value.nil? || deserialize_entry(value, **options).expired?
             end
           else
             written = entry_write(key, payload)
diff --git a/test/unit/solid_cache_test.rb b/test/unit/solid_cache_test.rb
index 2376345c..adec85ba 100644
--- a/test/unit/solid_cache_test.rb
+++ b/test/unit/solid_cache_test.rb
@@ -81,6 +81,23 @@ class SolidCacheFailsafeTest < ActiveSupport::TestCase
     @peek = lookup_store(expires_in: 60)
   end
 
+  test "write with unless_exist returns false when persistence fails" do
+    SolidCache::Entry.expects(:write).raises(ActiveRecord::Deadlocked)
+
+    assert_equal false, @cache.write("foo", "bar", unless_exist: true)
+    assert_nil @cache.read("foo")
+  end
+
+  test "failed write with unless_exist does not populate the local cache" do
+    SolidCache::Entry.expects(:write).raises(ActiveRecord::StatementTimeout)
+
+    @cache.with_local_cache do
+      @cache.write("foo", "bar", unless_exist: true)
+
+      assert_nil @cache.read("foo")
+    end
+  end
+
   def emulating_unavailability
     wait_for_background_tasks(@cache)
     emulating_timeouts do