Use the job class as the default concurrency key if none is provided

README.md

@@ -468,6 +468,14 @@ class MyJob < ApplicationJob
 
     # A unique key to be globally locked against.
     # Can be String or Lambda/Proc that is invoked in the context of the job.
+    #
+    # If a key is not provided GoodJob will create one for you. This key will be
+    # composed of the jobs class, the queue, and all passed arguments.
+    # `MyJob.set(queue: "special_queue").perform_later("Bob")` => 'MyJob-special_queue-["Bob"]'
+    # If you provide a custom concurrency key (for example, if one of your arguments
+    # is transient) make sure that it sufficiently unique across jobs and queues
+    # by adding the job class or queue to the key yourself, if needed.
+    #
     # Note: Arguments passed to #perform_later can be accessed through ActiveJob's `arguments` method
     # which is an array containing positional arguments and, optionally, a kwarg hash.
     key: -> { "MyJob-#{arguments.first}-#{arguments.last[:version]}" } #  MyJob.perform_later("Alice", version: 'v2') => "MyJob-Alice-v2"

lib/good_job/active_job_extensions/concurrency.rb

@@ -97,7 +97,7 @@ def good_job_concurrency_key
       # @return [Object] concurrency key
       def _good_job_concurrency_key
         key = self.class.good_job_concurrency_config[:key]
-        return if key.blank?
+        return "#{self.class.name}-#{queue_name}-#{ActiveJob::Arguments.serialize(arguments)}" if key.blank?
 
         key = instance_exec(&key) if key.respond_to?(:call)
         raise TypeError, "Concurrency key must be a String; was a #{key.class}" unless VALID_TYPES.any? { |type| key.is_a?(type) }

spec/lib/good_job/active_job_extensions/concurrency_spec.rb

@@ -194,6 +194,33 @@ def perform
       end
     end
 
+    context 'when no key is specified' do
+      before do
+        stub_const 'TestJob', (Class.new(ActiveJob::Base) do
+          include GoodJob::ActiveJobExtensions::Concurrency
+
+          def perform(name)
+          end
+        end)
+      end
+
+      it 'calculates a default concurrency key' do
+        job = TestJob.perform_later("Alice")
+        expect(job.good_job_concurrency_key).to eq('TestJob-default-["Alice"]')
+      end
+
+      it 'uses the overwritten queue name in the key' do
+        job = TestJob.set(queue: "different").perform_later("Alice")
+        expect(job.good_job_concurrency_key).to eq('TestJob-different-["Alice"]')
+      end
+
+      it 'works with complex parameters' do
+        execution = GoodJob::Execution.create(active_job_id: SecureRandom.uuid, queue_name: "default")
+        job = TestJob.perform_later(execution)
+        expect(job.good_job_concurrency_key).to eq("TestJob-default-[{\"_aj_globalid\"=>\"#{execution.to_global_id}\"}]")
+      end
+    end
+
     describe '#perform_later' do
       before do
         stub_const 'TestJob', (Class.new(ActiveJob::Base) do