Refactor options for middleware

Right now we only have one option that's supported, the delay. However I
can see us supporting other options in the future.

This PR refactors the options to get passed into the resolver so whether
you're using middleware or using the config options you can pass options
to the resolver. This will also make it easy to add new options in the
future.

4 files changed, 61 insertions, 11 deletions

diff --git a/activerecord/lib/active_record/middleware/database_selector.rb b/activerecord/lib/active_record/middleware/database_selector.rb
index adcfca4f8d..3ab50f5f6b 100644
--- a/activerecord/lib/active_record/middleware/database_selector.rb
+++ b/activerecord/lib/active_record/middleware/database_selector.rb
@@ -35,13 +35,14 @@ module ActiveRecord
     #   config.active_record.database_resolver = MyResolver
     #   config.active_record.database_operations = MyResolver::MySession
     class DatabaseSelector
-      def initialize(app, resolver_klass = Resolver, operations_klass = Resolver::Session)
+      def initialize(app, resolver_klass = Resolver, operations_klass = Resolver::Session, options = {})
         @app = app
         @resolver_klass = resolver_klass
         @operations_klass = operations_klass
+        @options = options
       end
 
-      attr_reader :resolver_klass, :operations_klass
+      attr_reader :resolver_klass, :operations_klass, :options
 
       # Middleware that determines which database connection to use in a multiple
       # database application.
@@ -57,7 +58,7 @@ module ActiveRecord
 
         def select_database(request, &blk)
           operations = operations_klass.build(request)
-          database_resolver = resolver_klass.call(operations)
+          database_resolver = resolver_klass.call(operations, options)
 
           if reading_request?(request)
             database_resolver.read(&blk)
diff --git a/activerecord/lib/active_record/middleware/database_selector/resolver.rb b/activerecord/lib/active_record/middleware/database_selector/resolver.rb
index acdb9b3238..0eeb0453ef 100644
--- a/activerecord/lib/active_record/middleware/database_selector/resolver.rb
+++ b/activerecord/lib/active_record/middleware/database_selector/resolver.rb
@@ -18,16 +18,18 @@ module ActiveRecord
       class Resolver # :nodoc:
         SEND_TO_REPLICA_DELAY = 2.seconds
 
-        def self.call(resolver)
-          new(resolver)
+        def self.call(resolver, options = {})
+          new(resolver, options)
         end
 
-        def initialize(resolver)
+        def initialize(resolver, options = {})
           @resolver = resolver
+          @options = options
+          @delay = @options && @options[:delay] ? @options[:delay] : SEND_TO_REPLICA_DELAY
           @instrumenter = ActiveSupport::Notifications.instrumenter
         end
 
-        attr_reader :resolver, :instrumenter
+        attr_reader :resolver, :delay, :instrumenter
 
         def read(&blk)
           if read_from_primary?
@@ -76,8 +78,7 @@ module ActiveRecord
           end
 
           def send_to_replica_delay
-            (ActiveRecord::Base.database_selector && ActiveRecord::Base.database_selector[:delay]) ||
-              SEND_TO_REPLICA_DELAY
+            delay
           end
 
           def time_since_last_write_ok?
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index a981fa97d9..017e279080 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -89,10 +89,10 @@ module ActiveRecord
     end
 
     initializer "active_record.database_selector" do
-      if config.active_record.database_selector
+      if options = config.active_record.delete(:database_selector)
         resolver = config.active_record.delete(:database_resolver)
         operations = config.active_record.delete(:database_operations)
-        config.app_middleware.use ActiveRecord::Middleware::DatabaseSelector, resolver, operations
+        config.app_middleware.use ActiveRecord::Middleware::DatabaseSelector, resolver, operations, options
       end
     end
 
diff --git a/activerecord/test/cases/database_selector_test.rb b/activerecord/test/cases/database_selector_test.rb
index 6142e223ce..4106a6ec46 100644
--- a/activerecord/test/cases/database_selector_test.rb
+++ b/activerecord/test/cases/database_selector_test.rb
@@ -95,6 +95,54 @@ module ActiveRecord
       assert @session_store[:last_write]
     end
 
+    def test_read_from_primary_with_options
+      resolver = ActiveRecord::Middleware::DatabaseSelector::Resolver.new(@session, delay: 5.seconds)
+
+      # Session should start empty
+      assert_nil @session_store[:last_write]
+
+      called = false
+      resolver.write do
+        assert ActiveRecord::Base.connected_to?(role: :writing)
+        called = true
+      end
+      assert called
+
+      # and be populated by the last write time
+      assert @session_store[:last_write]
+
+      read = false
+      resolver.read do
+        assert ActiveRecord::Base.connected_to?(role: :writing)
+        read = true
+      end
+      assert read
+    end
+
+    def test_read_from_replica_with_no_delay
+      resolver = ActiveRecord::Middleware::DatabaseSelector::Resolver.new(@session, delay: 0.seconds)
+
+      # Session should start empty
+      assert_nil @session_store[:last_write]
+
+      called = false
+      resolver.write do
+        assert ActiveRecord::Base.connected_to?(role: :writing)
+        called = true
+      end
+      assert called
+
+      # and be populated by the last write time
+      assert @session_store[:last_write]
+
+      read = false
+      resolver.read do
+        assert ActiveRecord::Base.connected_to?(role: :reading)
+        read = true
+      end
+      assert read
+    end
+
     def test_the_middleware_chooses_writing_role_with_POST_request
       middleware = ActiveRecord::Middleware::DatabaseSelector.new(lambda { |env|
         assert ActiveRecord::Base.connected_to?(role: :writing)