Rearrange stage event methods

This change rearranges the stage event methods by keeping the event
columns in an array.

ee/lib/gitlab/analytics/cycle_analytics/stage_events/issue_closed.rb

@@ -17,8 +17,8 @@ module Gitlab
             Issue
           end
 
-          def timestamp_projection
-            issue_table[:closed_at]
+          def column_list
+            [issue_table[:closed_at]]
           end
         end
       end

ee/lib/gitlab/analytics/cycle_analytics/stage_events/issue_first_added_to_board.rb

@@ -17,8 +17,8 @@ module Gitlab
             Issue
           end
 
-          def timestamp_projection
-            issue_metrics_table[:first_added_to_board_at]
+          def column_list
+            [issue_metrics_table[:first_added_to_board_at]]
           end
         end
       end

ee/lib/gitlab/analytics/cycle_analytics/stage_events/issue_first_associated_with_milestone.rb

@@ -17,8 +17,8 @@ module Gitlab
             Issue
           end
 
-          def timestamp_projection
-            issue_metrics_table[:first_associated_with_milestone_at]
+          def column_list
+            [issue_metrics_table[:first_associated_with_milestone_at]]
           end
         end
       end

ee/lib/gitlab/analytics/cycle_analytics/stage_events/issue_last_edited.rb

@@ -17,8 +17,8 @@ module Gitlab
             Issue
           end
 
-          def timestamp_projection
-            issue_table[:last_edited_at]
+          def column_list
+            [issue_table[:last_edited_at]]
           end
         end
       end

ee/lib/gitlab/analytics/cycle_analytics/stage_events/label_based_stage_event.rb

@@ -20,13 +20,8 @@ module Gitlab
             true
           end
 
-          def timestamp_projection
-            Arel.sql("#{join_expression_name}.created_at")
-          end
-
-          override :column_list
           def column_list
-            [timestamp_projection]
+            [Arel.sql("#{join_expression_name}.created_at")]
           end
 
           # rubocop: disable CodeReuse/ActiveRecord

ee/lib/gitlab/analytics/cycle_analytics/stage_events/merge_request_closed.rb

@@ -17,8 +17,8 @@ module Gitlab
             MergeRequest
           end
 
-          def timestamp_projection
-            mr_metrics_table[:latest_closed_at]
+          def column_list
+            [mr_metrics_table[:latest_closed_at]]
           end
         end
       end

ee/lib/gitlab/analytics/cycle_analytics/stage_events/merge_request_first_commit_at.rb

@@ -17,8 +17,8 @@ module Gitlab
             MergeRequest
           end
 
-          def timestamp_projection
-            mr_metrics_table[:first_commit_at]
+          def column_list
+            [mr_metrics_table[:first_commit_at]]
           end
         end
       end

ee/lib/gitlab/analytics/cycle_analytics/stage_events/merge_request_last_edited.rb

@@ -17,8 +17,8 @@ module Gitlab
             MergeRequest
           end
 
-          def timestamp_projection
-            mr_table[:last_edited_at]
+          def column_list
+            [mr_table[:last_edited_at]]
           end
         end
       end

lib/gitlab/analytics/cycle_analytics/stage_events/code_stage_start.rb

@@ -17,11 +17,6 @@ module Gitlab
             MergeRequest
           end
 
-          def timestamp_projection
-            Arel::Nodes::NamedFunction.new('COALESCE', column_list)
-          end
-
-          override :column_list
           def column_list
             [
               issue_metrics_table[:first_mentioned_in_commit_at],

lib/gitlab/analytics/cycle_analytics/stage_events/issue_created.rb

@@ -17,8 +17,8 @@ module Gitlab
             Issue
           end
 
-          def timestamp_projection
-            issue_table[:created_at]
+          def column_list
+            [issue_table[:created_at]]
           end
         end
       end

lib/gitlab/analytics/cycle_analytics/stage_events/issue_deployed_to_production.rb

@@ -17,13 +17,8 @@ module Gitlab
             Issue
           end
 
-          def timestamp_projection
-            mr_metrics_table[:first_deployed_to_production_at]
-          end
-
-          override :column_list
           def column_list
-            [timestamp_projection]
+            [mr_metrics_table[:first_deployed_to_production_at]]
           end
 
           # rubocop: disable CodeReuse/ActiveRecord

lib/gitlab/analytics/cycle_analytics/stage_events/issue_first_mentioned_in_commit.rb

@@ -17,8 +17,8 @@ module Gitlab
             Issue
           end
 
-          def timestamp_projection
-            issue_metrics_table[:first_mentioned_in_commit_at]
+          def column_list
+            [issue_metrics_table[:first_mentioned_in_commit_at]]
           end
         end
       end

lib/gitlab/analytics/cycle_analytics/stage_events/issue_stage_end.rb

@@ -17,11 +17,6 @@ module Gitlab
             Issue
           end
 
-          def timestamp_projection
-            Arel::Nodes::NamedFunction.new('COALESCE', column_list)
-          end
-
-          override :column_list
           def column_list
             [
               issue_metrics_table[:first_associated_with_milestone_at],

lib/gitlab/analytics/cycle_analytics/stage_events/merge_request_created.rb

@@ -17,8 +17,8 @@ module Gitlab
             MergeRequest
           end
 
-          def timestamp_projection
-            mr_table[:created_at]
+          def column_list
+            [mr_table[:created_at]]
           end
         end
       end

lib/gitlab/analytics/cycle_analytics/stage_events/merge_request_first_deployed_to_production.rb

@@ -17,8 +17,8 @@ module Gitlab
             MergeRequest
           end
 
-          def timestamp_projection
-            mr_metrics_table[:first_deployed_to_production_at]
+          def column_list
+            [mr_metrics_table[:first_deployed_to_production_at]]
           end
 
           # rubocop: disable CodeReuse/ActiveRecord

lib/gitlab/analytics/cycle_analytics/stage_events/merge_request_last_build_finished.rb

@@ -17,8 +17,8 @@ module Gitlab
             MergeRequest
           end
 
-          def timestamp_projection
-            mr_metrics_table[:latest_build_finished_at]
+          def column_list
+            [mr_metrics_table[:latest_build_finished_at]]
           end
         end
       end

lib/gitlab/analytics/cycle_analytics/stage_events/merge_request_last_build_started.rb

@@ -17,8 +17,8 @@ module Gitlab
             MergeRequest
           end
 
-          def timestamp_projection
-            mr_metrics_table[:latest_build_started_at]
+          def column_list
+            [mr_metrics_table[:latest_build_started_at]]
           end
         end
       end

lib/gitlab/analytics/cycle_analytics/stage_events/merge_request_merged.rb

@@ -17,8 +17,8 @@ module Gitlab
             MergeRequest
           end
 
-          def timestamp_projection
-            mr_metrics_table[:merged_at]
+          def column_list
+            [mr_metrics_table[:merged_at]]
           end
         end
       end

lib/gitlab/analytics/cycle_analytics/stage_events/metrics_based_stage_event.rb

@@ -11,7 +11,6 @@ module Gitlab
           end
           # rubocop: enable CodeReuse/ActiveRecord
 
-          override :column_list
           def column_list
             [timestamp_projection]
           end

lib/gitlab/analytics/cycle_analytics/stage_events/plan_stage_start.rb

@@ -17,11 +17,6 @@ module Gitlab
             Issue
           end
 
-          def timestamp_projection
-            Arel::Nodes::NamedFunction.new('COALESCE', column_list)
-          end
-
-          override :column_list
           def column_list
             [
               issue_metrics_table[:first_associated_with_milestone_at],

lib/gitlab/analytics/cycle_analytics/stage_events/stage_event.rb

@@ -34,14 +34,16 @@ module Gitlab
           # Each StageEvent must expose a timestamp or a timestamp like expression in order to build a range query.
           # Example: get me all the Issue records between start event end end event
           def timestamp_projection
-            raise NotImplementedError
+            columns = column_list
+
+            columns.one? ? columns.first : Arel::Nodes::NamedFunction.new('COALESCE', columns)
           end
 
           # List of columns that are referenced in the `timestamp_projection` expression
           # Example timestamp projection: COALESCE(issue_metrics.created_at, issue_metrics.updated_at)
           # Expected column list: issue_metrics.created_at, issue_metrics.updated_at
           def column_list
-            []
+            raise NotImplementedError
           end
 
           # Optionally a StageEvent may apply additional filtering or join other tables on the base query.