WIP - refactored some arel queries

lib/gitlab/cycle_analytics/events_fetcher.rb

@@ -11,14 +11,21 @@ module Gitlab
       def fetch_issues
         cte_table = Arel::Table.new("cte_table_for_issue")
 
-        interval_query = Arel::Nodes::As.new(
-          cte_table,
-          subtract_datetimes(base_query_for(:issue), *attributes, 'issue'))
+        # Build a `SELECT` query. We find the first of the `end_time_attrs` that isn't `NULL` (call this end_time).
+        # Next, we find the first of the start_time_attrs that isn't `NULL` (call this start_time).
+        # We compute the (end_time - start_time) interval, and give it an alias based on the current
+        # cycle analytics stage.
 
-        #TODO ActiveRecord::Base.connection.execute(interval_query)
+        base_query = base_query_for(:issue)
+
+        diff_fn = subtract_datetimes_diff(base_query, issue_table[:created_at], metric_attributes)
+
+        query = base_query.project(diff_fn.as('issue_diff'))
+
+        ActiveRecord::Base.connection.execute(query.to_sql)
       end
 
-      def attributes
+      def metric_attributes
         [issue_metrics_table[:first_associated_with_milestone_at],
          issue_metrics_table[:first_added_to_board_at]]
       end

lib/gitlab/cycle_analytics/metrics_fetcher.rb

@@ -28,7 +28,7 @@ module Gitlab
       # automatically excluded.
       def base_query_for(name)
         # Load issues
-        query = issue_metrics_table.join(issue_table).on(issue_table[:id].eq(mr_closing_issues_table[:issue_id])).
+        query = mr_closing_issues_table.join(issue_table).on(issue_table[:id].eq(mr_closing_issues_table[:issue_id])).
           join(issue_metrics_table).on(issue_table[:id].eq(issue_metrics_table[:issue_id])).
           where(issue_table[:project_id].eq(@project.id)).
           where(issue_table[:deleted_at].eq(nil)).

lib/gitlab/database/date_time.rb

@@ -8,7 +8,13 @@ module Gitlab
       # Note: For MySQL, the interval is returned in seconds.
       #       For PostgreSQL, the interval is returned as an INTERVAL type.
       def subtract_datetimes(query_so_far, end_time_attrs, start_time_attrs, as)
-        diff_fn = if Gitlab::Database.postgresql?
+        diff_fn = subtract_datetimes_diff(query_so_far, end_time_attrs, start_time_attrs)
+
+        query_so_far.project(diff_fn.as(as))
+      end
+
+      def subtract_datetimes_diff(query_so_far, end_time_attrs, start_time_attrs)
+        if Gitlab::Database.postgresql?
           Arel::Nodes::Subtraction.new(
             Arel::Nodes::NamedFunction.new("COALESCE", Array.wrap(end_time_attrs)),
             Arel::Nodes::NamedFunction.new("COALESCE", Array.wrap(start_time_attrs)))
@@ -19,8 +25,6 @@ module Gitlab
              Arel::Nodes::NamedFunction.new("COALESCE", Array.wrap(start_time_attrs)),
              Arel::Nodes::NamedFunction.new("COALESCE", Array.wrap(end_time_attrs))])
         end
-
-        query_so_far.project(diff_fn.as(as))
       end
     end
   end

spec/lib/gitlab/cycle_analytics/events_spec.rb

@@ -15,12 +15,13 @@ describe Gitlab::CycleAnalytics::Events do
     let!(:context) { create(:issue, project: project) }
 
     xit 'does something' do
-      expect(subject.issue_events).to eq([])
+      expect(subject.issue_events).to eq([context])
     end
   end
 
   def setup(context)
-    create(:milestone, project: project)
+    milestone = create(:milestone, project: project)
+    context.update(milestone: milestone)
     create_merge_request_closing_issue(context)
   end
 end