Make `Migrator.current_version` work without a current database

This is necessary in order to make the processing dependent on
`Migrator.current_version` work even without database.

Context: https://github.com/rails/rails/pull/31135#issuecomment-348404326

1 files changed, 5 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index 9ee8425e1b..4538ed6a5f 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -90,12 +90,15 @@ module ActiveRecord
             filename = File.join(app.config.paths["db"].first, "schema_cache.yml")
 
             if File.file?(filename)
+              current_version = ActiveRecord::Migrator.current_version
+              next if current_version.nil?
+
               cache = YAML.load(File.read(filename))
-              if cache.version == ActiveRecord::Migrator.current_version
+              if cache.version == current_version
                 connection.schema_cache = cache
                 connection_pool.schema_cache = cache.dup
               else
-                warn "Ignoring db/schema_cache.yml because it has expired. The current schema version is #{ActiveRecord::Migrator.current_version}, but the one in the cache is #{cache.version}."
+                warn "Ignoring db/schema_cache.yml because it has expired. The current schema version is #{current_version}, but the one in the cache is #{cache.version}."
               end
             end
           end