RedisCacheStore: fix `#write_multi` mset serialization

Closes #31886
Fixes #31884

2 files changed, 18 insertions, 1 deletions

diff --git a/activesupport/lib/active_support/cache/redis_cache_store.rb b/activesupport/lib/active_support/cache/redis_cache_store.rb
index 1de98dcd6c..b5a2a2a636 100644
--- a/activesupport/lib/active_support/cache/redis_cache_store.rb
+++ b/activesupport/lib/active_support/cache/redis_cache_store.rb
@@ -17,6 +17,7 @@ end
 
 require "digest/sha2"
 require "active_support/core_ext/marshal"
+require "active_support/core_ext/hash/transform_values"
 
 module ActiveSupport
   module Cache
@@ -360,7 +361,13 @@ module ActiveSupport
           if entries.any?
             if mset_capable? && expires_in.nil?
               failsafe :write_multi_entries do
-                redis.mapped_mset(entries)
+                serialized_entries = if options[:raw]
+                  entries.transform_values { |e| e.value.to_s }
+                else
+                  entries.transform_values { |e| serialize_entry(e) }
+                end
+
+                redis.mapped_mset(serialized_entries)
               end
             else
               super
diff --git a/activesupport/test/cache/behaviors/cache_store_behavior.rb b/activesupport/test/cache/behaviors/cache_store_behavior.rb
index ac37ab6e61..efb57d34a2 100644
--- a/activesupport/test/cache/behaviors/cache_store_behavior.rb
+++ b/activesupport/test/cache/behaviors/cache_store_behavior.rb
@@ -113,6 +113,16 @@ module CacheStoreBehavior
     assert_equal("fufu", @cache.read("fu"))
   end
 
+  def test_fetch_multi_without_expires_in
+    @cache.write("foo", "bar")
+    @cache.write("fud", "biz")
+
+    values = @cache.fetch_multi("foo", "fu", "fud", expires_in: nil) { |value| value * 2 }
+
+    assert_equal({ "foo" => "bar", "fu" => "fufu", "fud" => "biz" }, values)
+    assert_equal("fufu", @cache.read("fu"))
+  end
+
   def test_multi_with_objects
     cache_struct = Struct.new(:cache_key, :title)
     foo = cache_struct.new("foo", "FOO!")