Treat ActiveRecord::Base and ApplicationRecord as "primary"

When someone has a multi-db application their `ApplicationRecord` will
look like:

```ruby
class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true

  connects_to database: { writing: :primary, reading: :replica }
end
```

This will cause us to open 2 connections to ActiveRecord::Base's
database when we actually only want 1. This is because Rails sees
`ApplicationRecord` and thinks it's a new connection, not the existing
`ActiveRecord::Base` connection because the
`connection_specification_name` is different.

This PR changes `ApplicationRecord` classes to consider themselves the
same as the "primary" connection.

Fixes #36382

1 files changed, 3 insertions, 3 deletions

diff --git a/railties/test/application/loading_test.rb b/railties/test/application/loading_test.rb
index 9c98489590..322a6e1ca0 100644
--- a/railties/test/application/loading_test.rb
+++ b/railties/test/application/loading_test.rb
@@ -116,7 +116,7 @@ class LoadingTest < ActiveSupport::TestCase
     RUBY
 
     app_file "app/models/post.rb", <<-MODEL
-      class Post < ActiveRecord::Base
+      class Post < ApplicationRecord
       end
     MODEL
 
@@ -133,9 +133,9 @@ class LoadingTest < ActiveSupport::TestCase
     require "#{rails_root}/config/environment"
     setup_ar!
 
-    assert_equal [ActiveStorage::Blob, ActiveStorage::Attachment, ActiveRecord::SchemaMigration, ActiveRecord::InternalMetadata].collect(&:to_s).sort, ActiveRecord::Base.descendants.collect(&:to_s).sort
+    assert_equal [ActiveStorage::Blob, ActiveStorage::Attachment, ActiveRecord::SchemaMigration, ActiveRecord::InternalMetadata, ApplicationRecord].collect(&:to_s).sort, ActiveRecord::Base.descendants.collect(&:to_s).sort
     get "/load"
-    assert_equal [ActiveStorage::Blob, ActiveStorage::Attachment, ActiveRecord::SchemaMigration, ActiveRecord::InternalMetadata, Post].collect(&:to_s).sort, ActiveRecord::Base.descendants.collect(&:to_s).sort
+    assert_equal [ActiveStorage::Blob, ActiveStorage::Attachment, ActiveRecord::SchemaMigration, ActiveRecord::InternalMetadata, ApplicationRecord, Post].collect(&:to_s).sort, ActiveRecord::Base.descendants.collect(&:to_s).sort
     get "/unload"
     assert_equal [ActiveStorage::Blob, ActiveStorage::Attachment, ActiveRecord::SchemaMigration, ActiveRecord::InternalMetadata].collect(&:to_s).sort, ActiveRecord::Base.descendants.collect(&:to_s).sort
   end