Prevent processing events when different version is activating

During activation the last existing events are replayed before the
projector is marked active. Block new events since they will not be
picked up by the replay process.

Author: erikrozendaal

lib/sequent/core/event_publisher.rb

@@ -5,7 +5,7 @@ module Core
     class ProjectorMigrationError < RuntimeError; end
     class UnknownActiveProjectorError < ProjectorMigrationError; end
     class ReplayingProjectorMismatchError < ProjectorMigrationError; end
-    class NewerProjectorIsActiveError < ProjectorMigrationError; end
+    class DifferentProjectorVersionIsActiveError < ProjectorMigrationError; end
 
     #
     # EventPublisher ensures that, for every thread, events will be published

lib/sequent/core/projector.rb

@@ -206,12 +206,19 @@ def is_active?
         projector_state = Projectors.projector_states[self.class.name]
         return false if projector_state.nil?
 
-        return true if projector_state.active_version == version
-
-        # Replaying or activating the current version, so run this projector (it will write to a temporary table).
-        return true if projector_state.replaying_version == version || projector_state.activating_version == version
+        if projector_state.activating_version.present?
+          # Current projector version is activating, so we write to the temporary replay table.
+          return true if projector_state.activating_version == version
+        else
+          return true if projector_state.active_version == version
+
+          # Replaying the current version, so run this projector (it will write to a temporary table).
+          return true if projector_state.replaying_version == version
+        end
 
-        fail NewerProjectorIsActiveError,
+        # A different projector version is active or activating, so we cannot write new events since they will
+        # not be properly propagated.
+        fail DifferentProjectorVersionIsActiveError,
              "projector #{self.class} version #{version} does not match state #{projector_state}"
       end
     end

spec/lib/sequent/core/event_publisher_spec.rb

@@ -84,22 +84,24 @@ class UnknownProjector < Sequent::Core::Projector
       Sequent.configuration.event_handlers << TestEventHandler.new
       Sequent.configuration.command_handlers << TestCommandHandler.new
       Sequent.configuration.migrations_class = SpecMigrations
+      Sequent.configuration.migrations_class.version = 0
+      Sequent.activate_current_configuration!
     end
 
     it 'fails when unknown projectors are active' do
-      Sequent::Core::Projectors.register_active_projectors!([TestEventHandler, UnknownProjector], 1)
+      Sequent::Core::Projectors.register_active_projectors!([TestEventHandler, UnknownProjector], 0)
 
       expect do
         Sequent.command_service.execute_commands TriggerTestCase.new(aggregate_id: Sequent.new_uuid)
       end.to raise_error Sequent::Core::UnknownActiveProjectorError
     end
 
-    it 'fails when newer version of the projector is activating' do
+    it 'fails when different version of the projector is activating' do
       Sequent::Core::Projectors.register_activating_projectors!([TestEventHandler], Sequent.new_version + 1)
 
       expect do
         Sequent.command_service.execute_commands TriggerTestCase.new(aggregate_id: Sequent.new_uuid)
-      end.to raise_error Sequent::Core::NewerProjectorIsActiveError
+      end.to raise_error Sequent::Core::DifferentProjectorVersionIsActiveError
     end
   end
 end