Disable multi-db for SQLite

app/models/application_record.rb

@@ -1,12 +1,7 @@
 class ApplicationRecord < ActiveRecord::Base
   primary_abstract_class
 
-  # SQLite doesn't use separate replica databases
-  if ENV.fetch("DATABASE_ADAPTER", "mysql") == "sqlite"
-    connects_to database: { writing: :primary, reading: :primary }
-  else
-    connects_to database: { writing: :primary, reading: :replica }
-  end
+  configure_replica_connections
 
   attribute :id, :uuid, default: -> { ActiveRecord::Type::Uuid.generate }
 end

config/initializers/active_storage.rb

@@ -4,14 +4,8 @@ ActiveSupport.on_load(:active_storage_blob) do
   end
 end
 
-# Use DB read/write splitting for Active Storage models
 ActiveSupport.on_load(:active_storage_record) do
-  # SQLite doesn't use separate replica databases
-  if ENV.fetch("DATABASE_ADAPTER", "mysql") == "sqlite"
-    connects_to database: { writing: :primary, reading: :primary }
-  else
-    connects_to database: { writing: :primary, reading: :replica }
-  end
+  configure_replica_connections
 end
 
 module ActiveStorageControllerExtensions

config/initializers/database_role_logging.rb

@@ -1,3 +1,5 @@
+require_relative "extensions"
+
 class DatabaseRoleLogger
   def initialize(app)
     @app = app
@@ -10,4 +12,6 @@ class DatabaseRoleLogger
   end
 end
 
+if ActiveRecord::Base.replica_configured?
   Rails.application.config.middleware.insert_after ActiveRecord::Middleware::DatabaseSelector, DatabaseRoleLogger
+end

config/initializers/multi_db.rb

@@ -1,7 +1,10 @@
 require "deployment"
+require_relative "extensions"
 
+if ActiveRecord::Base.replica_configured?
   Rails.application.configure do
     config.active_record.database_selector = { delay: 1.second }
     config.active_record.database_resolver = Deployment::DatabaseResolver
     config.active_record.database_resolver_context = ActiveRecord::Middleware::DatabaseSelector::Resolver::Session
   end
+end

config/initializers/tenanting/account_slug.rb

@@ -43,6 +43,4 @@ module AccountSlug
   def self.encode(id) FORMAT % id end
 end
 
-Rails.application.config.middleware.tap do |stack|
-  stack.insert_before ActiveRecord::Middleware::DatabaseSelector, AccountSlug::Extractor
-end
+Rails.application.config.middleware.insert_after Rack::TempfileReaper, AccountSlug::Extractor

lib/rails_ext/active_record_replica_support.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+# Adds a helper method to check if replica database connections are configured
+# and automatically configures read/write splitting when replicas are available.
+#
+# Usage:
+#   class ApplicationRecord < ActiveRecord::Base
+#     configure_replica_connections
+#   end
+module ActiveRecordReplicaSupport
+  extend ActiveSupport::Concern
+
+  class_methods do
+    # Automatically configures connects_to for read/write splitting if a replica
+    # database is configured for the current environment. This is a no-op if no
+    # replica configuration exists.
+    #
+    # Example:
+    #   class ApplicationRecord < ActiveRecord::Base
+    #     configure_replica_connections
+    #   end
+    def configure_replica_connections
+      if replica_configured?
+        connects_to database: { writing: :primary, reading: :replica }
+      end
+    end
+
+    # Returns true if a replica database configuration exists for the current
+    # environment. This allows different database adapters to opt in or out of
+    # read/write splitting based on their database.yml configuration.
+    #
+    # Example:
+    #   ApplicationRecord.replica_configured? # => true for MySQL, false for SQLite
+    def replica_configured?
+      configurations.find_db_config("replica").present?
+    end
+  end
+end
+
+ActiveRecord::Base.include ActiveRecordReplicaSupport