Make `reading_role` and `writing_role` module instance variables

Followup: https://github.com/rails/rails/pull/42442

activerecord/lib/active_record.rb

@@ -179,6 +179,12 @@ module ActiveRecord
   singleton_class.attr_accessor :default_timezone
   self.default_timezone = :utc
 
+  singleton_class.attr_accessor :writing_role
+  self.writing_role = :writing
+
+  singleton_class.attr_accessor :reading_role
+  self.reading_role = :reading
+
   def self.eager_load!
     super
     ActiveRecord::Locking.eager_load!

activerecord/lib/active_record/connection_handling.rb

@@ -184,7 +184,7 @@ module ActiveRecord
         raise NotImplementedError, "connected_to_many can only be called on ActiveRecord::Base."
       end
 
-      prevent_writes = true if role == reading_role
+      prevent_writes = true if role == ActiveRecord.reading_role
 
       connected_to_stack << { role: role, shard: shard, prevent_writes: prevent_writes, klasses: classes }
       yield
@@ -204,7 +204,7 @@ module ActiveRecord
         raise NotImplementedError, "`connecting_to` is not available with `legacy_connection_handling`."
       end
 
-      prevent_writes = true if role == reading_role
+      prevent_writes = true if role == ActiveRecord.reading_role
 
       self.connected_to_stack << { role: role, shard: shard, prevent_writes: prevent_writes, klasses: [self] }
     end
@@ -240,7 +240,7 @@ module ActiveRecord
 
     def lookup_connection_handler(handler_key) # :nodoc:
       if ActiveRecord.legacy_connection_handling
-        handler_key ||= ActiveRecord::Base.writing_role
+        handler_key ||= ActiveRecord.writing_role
         connection_handlers[handler_key] ||= ActiveRecord::ConnectionAdapters::ConnectionHandler.new
       else
         ActiveRecord::Base.connection_handler
@@ -356,7 +356,7 @@ module ActiveRecord
       end
 
       def with_role_and_shard(role, shard, prevent_writes)
-        prevent_writes = true if role == reading_role
+        prevent_writes = true if role == ActiveRecord.reading_role
 
         if ActiveRecord.legacy_connection_handling
           with_handler(role.to_sym) do

activerecord/lib/active_record/core.rb

@@ -144,10 +144,6 @@ module ActiveRecord
       class_attribute :strict_loading_by_default, instance_accessor: false, default: false
       class_attribute :strict_loading_mode, instance_accessor: true, default: :all
 
-      mattr_accessor :writing_role, instance_accessor: false, default: :writing
-
-      mattr_accessor :reading_role, instance_accessor: false, default: :reading
-
       class_attribute :has_many_inversing, instance_accessor: false, default: false
 
       mattr_accessor :sqlite3_production_warning, instance_accessor: false, default: true
@@ -357,7 +353,7 @@ module ActiveRecord
       end
 
       self.default_connection_handler = ConnectionAdapters::ConnectionHandler.new
-      self.default_role = writing_role
+      self.default_role = ActiveRecord.writing_role
       self.default_shard = :default
 
       def self.strict_loading_violation!(owner:, reflection:) # :nodoc:
@@ -459,6 +455,22 @@ module ActiveRecord
         ActiveRecord.default_timezone
       end
 
+      def reading_role # :nodoc:
+        ActiveSupport::Deprecation.warn(<<~MSG)
+          ActiveRecord::Base.reading_role is deprecated and will be removed in Rails 7.0.
+          Use `ActiveRecord.reading_role` instead.
+        MSG
+        ActiveRecord.reading_role
+      end
+
+      def writing_role # :nodoc:
+        ActiveSupport::Deprecation.warn(<<~MSG)
+          ActiveRecord::Base.writing_role is deprecated and will be removed in Rails 7.0.
+          Use `ActiveRecord.writing_role` instead.
+        MSG
+        ActiveRecord.writing_role
+      end
+
       def initialize_generated_modules # :nodoc:
         generated_association_methods
       end

activerecord/lib/active_record/middleware/database_selector/resolver.rb

@@ -50,7 +50,7 @@ module ActiveRecord
 
         private
           def read_from_primary(&blk)
-            ActiveRecord::Base.connected_to(role: ActiveRecord::Base.writing_role, prevent_writes: true) do
+            ActiveRecord::Base.connected_to(role: ActiveRecord.writing_role, prevent_writes: true) do
               instrumenter.instrument("database_selector.active_record.read_from_primary") do
                 yield
               end
@@ -58,7 +58,7 @@ module ActiveRecord
           end
 
           def read_from_replica(&blk)
-            ActiveRecord::Base.connected_to(role: ActiveRecord::Base.reading_role, prevent_writes: true) do
+            ActiveRecord::Base.connected_to(role: ActiveRecord.reading_role, prevent_writes: true) do
               instrumenter.instrument("database_selector.active_record.read_from_replica") do
                 yield
               end
@@ -66,7 +66,7 @@ module ActiveRecord
           end
 
           def write_to_primary(&blk)
-            ActiveRecord::Base.connected_to(role: ActiveRecord::Base.writing_role, prevent_writes: false) do
+            ActiveRecord::Base.connected_to(role: ActiveRecord.writing_role, prevent_writes: false) do
               instrumenter.instrument("database_selector.active_record.wrote_to_primary") do
                 yield
               ensure

activerecord/lib/active_record/railtie.rb

@@ -224,7 +224,7 @@ To keep using the current cache store, you can turn off cache versioning entirel
     initializer "active_record.initialize_database" do
       ActiveSupport.on_load(:active_record) do
         if ActiveRecord.legacy_connection_handling
-          self.connection_handlers = { writing_role => ActiveRecord::Base.default_connection_handler }
+          self.connection_handlers = { ActiveRecord.writing_role => ActiveRecord::Base.default_connection_handler }
         end
         self.configurations = Rails.application.config.database_configuration
 

activerecord/lib/active_record/test_fixtures.rb

@@ -194,7 +194,7 @@ module ActiveRecord
       # can see data in the open transaction on the writing connection.
       def setup_shared_connection_pool
         if ActiveRecord.legacy_connection_handling
-          writing_handler = ActiveRecord::Base.connection_handlers[ActiveRecord::Base.writing_role]
+          writing_handler = ActiveRecord::Base.connection_handlers[ActiveRecord.writing_role]
 
           ActiveRecord::Base.connection_handlers.values.each do |handler|
             if handler != writing_handler
@@ -221,7 +221,7 @@ module ActiveRecord
           handler.connection_pool_names.each do |name|
             pool_manager = handler.send(:owner_to_pool_manager)[name]
             pool_manager.shard_names.each do |shard_name|
-              writing_pool_config = pool_manager.get_pool_config(ActiveRecord::Base.writing_role, shard_name)
+              writing_pool_config = pool_manager.get_pool_config(ActiveRecord.writing_role, shard_name)
               @saved_pool_configs[name][shard_name] ||= {}
               pool_manager.role_names.each do |role|
                 next unless pool_config = pool_manager.get_pool_config(role, shard_name)

activerecord/lib/rails/generators/active_record/model/templates/abstract_base_class.rb.tt

@@ -2,6 +2,6 @@
 class <%= abstract_class_name %> < ApplicationRecord
   self.abstract_class = true
 
-  connects_to database: { <%= ActiveRecord::Base.writing_role %>: :<%= database -%> }
+  connects_to database: { <%= ActiveRecord.writing_role %>: :<%= database -%> }
 end
 <% end -%>

activerecord/test/cases/connection_adapters/connection_handler_test.rb

@@ -285,8 +285,8 @@ module ActiveRecord
       end
 
       def test_default_handlers_are_writing_and_reading
-        assert_equal :writing, ActiveRecord::Base.writing_role
-        assert_equal :reading, ActiveRecord::Base.reading_role
+        assert_equal :writing, ActiveRecord.writing_role
+        assert_equal :reading, ActiveRecord.reading_role
       end
 
       if Process.respond_to?(:fork)

activerecord/test/cases/connection_adapters/connection_handlers_multi_db_test.rb

@@ -362,21 +362,21 @@ module ActiveRecord
       end
 
       def test_default_handlers_are_writing_and_reading
-        assert_equal :writing, ActiveRecord::Base.writing_role
-        assert_equal :reading, ActiveRecord::Base.reading_role
+        assert_equal :writing, ActiveRecord.writing_role
+        assert_equal :reading, ActiveRecord.reading_role
       end
 
       def test_an_application_can_change_the_default_handlers
-        old_writing = ActiveRecord::Base.writing_role
-        old_reading = ActiveRecord::Base.reading_role
-        ActiveRecord::Base.writing_role = :default
-        ActiveRecord::Base.reading_role = :readonly
+        old_writing = ActiveRecord.writing_role
+        old_reading = ActiveRecord.reading_role
+        ActiveRecord.writing_role = :default
+        ActiveRecord.reading_role = :readonly
 
-        assert_equal :default, ActiveRecord::Base.writing_role
-        assert_equal :readonly, ActiveRecord::Base.reading_role
+        assert_equal :default, ActiveRecord.writing_role
+        assert_equal :readonly, ActiveRecord.reading_role
       ensure
-        ActiveRecord::Base.writing_role = old_writing
-        ActiveRecord::Base.reading_role = old_reading
+        ActiveRecord.writing_role = old_writing
+        ActiveRecord.reading_role = old_reading
       end
     end
   end

activerecord/test/cases/connection_adapters/legacy_connection_handlers_multi_db_test.rb

@@ -424,21 +424,21 @@ module ActiveRecord
       end
 
       def test_default_handlers_are_writing_and_reading
-        assert_equal :writing, ActiveRecord::Base.writing_role
-        assert_equal :reading, ActiveRecord::Base.reading_role
+        assert_equal :writing, ActiveRecord.writing_role
+        assert_equal :reading, ActiveRecord.reading_role
       end
 
       def test_an_application_can_change_the_default_handlers
-        old_writing = ActiveRecord::Base.writing_role
-        old_reading = ActiveRecord::Base.reading_role
-        ActiveRecord::Base.writing_role = :default
-        ActiveRecord::Base.reading_role = :readonly
+        old_writing = ActiveRecord.writing_role
+        old_reading = ActiveRecord.reading_role
+        ActiveRecord.writing_role = :default
+        ActiveRecord.reading_role = :readonly
 
-        assert_equal :default, ActiveRecord::Base.writing_role
-        assert_equal :readonly, ActiveRecord::Base.reading_role
+        assert_equal :default, ActiveRecord.writing_role
+        assert_equal :readonly, ActiveRecord.reading_role
       ensure
-        ActiveRecord::Base.writing_role = old_writing
-        ActiveRecord::Base.reading_role = old_reading
+        ActiveRecord.writing_role = old_writing
+        ActiveRecord.reading_role = old_reading
       end
     end
   end

activerecord/test/cases/query_cache_test.rb

@@ -760,7 +760,7 @@ class QueryCacheTest < ActiveRecord::TestCase
 
   private
     def with_temporary_connection_pool
-      pool_config = ActiveRecord::Base.connection_handler.send(:owner_to_pool_manager).fetch("ActiveRecord::Base").get_pool_config(ActiveRecord::Base.writing_role, :default)
+      pool_config = ActiveRecord::Base.connection_handler.send(:owner_to_pool_manager).fetch("ActiveRecord::Base").get_pool_config(ActiveRecord.writing_role, :default)
       new_pool = ActiveRecord::ConnectionAdapters::ConnectionPool.new(pool_config)
 
       pool_config.stub(:pool, new_pool) do

activestorage/app/models/active_storage/preview.rb

@@ -93,7 +93,7 @@ class ActiveStorage::Preview
 
     def process
       previewer.preview(service_name: blob.service_name) do |attachable|
-        ActiveRecord::Base.connected_to(role: ActiveRecord::Base.writing_role) do
+        ActiveRecord::Base.connected_to(role: ActiveRecord.writing_role) do
           image.attach(attachable)
         end
       end

activestorage/app/models/active_storage/variant_with_record.rb

@@ -41,7 +41,7 @@ class ActiveStorage::VariantWithRecord
 
     def create_or_find_record(image:)
       @record =
-        ActiveRecord::Base.connected_to(role: ActiveRecord::Base.writing_role) do
+        ActiveRecord::Base.connected_to(role: ActiveRecord.writing_role) do
           blob.variant_records.create_or_find_by!(variation_digest: variation.digest) do |record|
             record.image.attach(image)
           end