Threadsafe "with_transactional_batching" block method (#29)

This adds a `Journaled.with_transactional_batching { }` feature that can be used to conditionally enable batching within the current thread, even if the feature is disabled globally.

README.md

@@ -682,6 +682,14 @@ This feature can be disabled conditionally:
 Journaled.transactional_batching_enabled = false
 ```
 
+And can then be enabled via the following block:
+
+```ruby
+Journaled.with_transactional_batching do
+  # your code
+end
+```
+
 Backwards compatibility has been included for background jobs enqueued by
 version 4.0 and above, but **has been dropped for jobs emitted by versions prior
 to 4.0**. (Again, be sure to upgrade only one major version at a time.)

lib/journaled.rb

@@ -16,7 +16,19 @@ module Journaled
   mattr_accessor(:http_open_timeout) { 2 }
   mattr_accessor(:http_read_timeout) { 60 }
   mattr_accessor(:job_base_class_name) { 'ActiveJob::Base' }
-  mattr_accessor(:transactional_batching_enabled) { true }
+  mattr_writer(:transactional_batching_enabled) { true }
+
+  def self.transactional_batching_enabled?
+    Thread.current[:journaled_transactional_batching_enabled] || @@transactional_batching_enabled
+  end
+
+  def self.with_transactional_batching
+    value_was = Thread.current[:journaled_transactional_batching_enabled]
+    Thread.current[:journaled_transactional_batching_enabled] = true
+    yield
+  ensure
+    Thread.current[:journaled_transactional_batching_enabled] = value_was
+  end
 
   def self.development_or_test?
     %w(development test).include?(Rails.env)

lib/journaled/audit_log.rb

@@ -83,7 +83,7 @@ def enabled?
 
       def dup
         super.tap do |config|
-          config.ignored_columns = ignored_columns.dup
+          config.ignored_columns = ignored_columns.dup # rubocop:disable Rails/IgnoredColumnsAssignment
           config.enqueue_opts = enqueue_opts.dup
         end
       end

lib/journaled/connection.rb

@@ -2,11 +2,11 @@ module Journaled
   module Connection
     class << self
       def available?
-        Journaled.transactional_batching_enabled && transaction_open?
+        Journaled.transactional_batching_enabled? && transaction_open?
       end
 
       def stage!(event)
-        raise TransactionSafetyError, <<~MSG unless transaction_open?
+        raise TransactionSafetyError, <<~MSG unless available?
           Transaction not available! By default, journaled event batching requires an open database transaction.
         MSG
 

lib/journaled/version.rb

@@ -1,3 +1,3 @@
 module Journaled
-  VERSION = "5.2.0".freeze
+  VERSION = "5.3.0".freeze
 end

spec/lib/journaled/connection_spec.rb

@@ -27,7 +27,7 @@
         end
       end
 
-      context 'when transactional batching is disabled' do
+      context 'when transactional batching is disabled globally' do
         around do |example|
           Journaled.transactional_batching_enabled = false
           example.run
@@ -36,8 +36,23 @@
         end
 
         it 'returns false, and raises an error when events are staged' do
-          expect(described_class.available?).to be false
-          expect { described_class.stage!(event) }.to raise_error(Journaled::TransactionSafetyError)
+          ActiveRecord::Base.transaction do
+            expect(described_class.available?).to be false
+            expect { described_class.stage!(event) }.to raise_error(Journaled::TransactionSafetyError)
+          end
+        end
+
+        context 'but thread-local batching is enabled' do
+          around do |example|
+            Journaled.with_transactional_batching { example.run }
+          end
+
+          it 'returns true, and allows for staging events' do
+            ActiveRecord::Base.transaction do
+              expect(described_class.available?).to be true
+              expect { described_class.stage!(event) }.not_to raise_error
+            end
+          end
         end
       end
     end

spec/models/journaled/writer_spec.rb

@@ -393,7 +393,7 @@ def fake_event(num)
         end
       end
 
-      context 'when transactional batching is disabled' do
+      context 'when transactional batching is disabled globally' do
         around do |example|
           Journaled.transactional_batching_enabled = false
           example.run
@@ -415,6 +415,27 @@ def fake_event(num)
             .and journal_event_including(id: 'FAKE_UUID_1', event_type: 'fake_event_1')
             .and journal_event_including(id: 'FAKE_UUID_5', event_type: 'fake_event_5')
         end
+
+        context 'but thread-local transactional batching is enabled' do
+          around do |example|
+            Journaled.with_transactional_batching { example.run }
+          end
+
+          it 'batches multiple events and does not enqueue until the end of a transaction' do
+            expect {
+              ActiveRecord::Base.transaction do
+                expect { described_class.new(journaled_event: fake_event(1)).journal! }
+                  .to not_change { enqueued_jobs.count }.from(0)
+                  .and not_journal_event_including(id: 'FAKE_UUID_1', event_type: 'fake_event_1')
+                expect { described_class.new(journaled_event: fake_event(2)).journal! }
+                  .to not_change { enqueued_jobs.count }.from(0)
+                  .and not_journal_event_including(id: 'FAKE_UUID_2', event_type: 'fake_event_2')
+              end
+            }.to change { enqueued_jobs.count }.from(0).to(1)
+              .and journal_event_including(id: 'FAKE_UUID_1', event_type: 'fake_event_1')
+              .and journal_event_including(id: 'FAKE_UUID_2', event_type: 'fake_event_2')
+          end
+        end
       end
 
       context 'when an event is enqueued in its own before_commit callback' do