1 files changed, 23 insertions, 20 deletions

diff --git a/app/models/event_collection.rb b/app/models/event_collection.rb
index a4c69b11781..4778f74568e 100644
--- a/app/models/event_collection.rb
+++ b/app/models/event_collection.rb
@@ -6,6 +6,8 @@
 # in a controller), it's not suitable for building queries that are used for
 # building other queries.
 class EventCollection
+  include Gitlab::Utils::StrongMemoize
+
   # To prevent users from putting too much pressure on the database by cycling
   # through thousands of events we put a limit on the number of pages.
   MAX_PAGE = 10
@@ -13,57 +15,52 @@ class EventCollection
   # projects - An ActiveRecord::Relation object that returns the projects for
   #            which to retrieve events.
   # filter - An EventFilter instance to use for filtering events.
-  def initialize(projects, limit: 20, offset: 0, filter: nil)
+  def initialize(projects, limit: 20, offset: 0, filter: nil, groups: nil)
     @projects = projects
     @limit = limit
     @offset = offset
     @filter = filter
+    @groups = groups
   end
 
   # Returns an Array containing the events.
   def to_a
     return [] if current_page > MAX_PAGE
 
-    relation = if Gitlab::Database.join_lateral_supported?
-                 relation_with_join_lateral
+    relation = if groups
+                 project_and_group_events
                else
-                 relation_without_join_lateral
+                 relation_with_join_lateral('project_id', projects)
                end
 
+    relation = paginate_events(relation)
     relation.with_associations.to_a
   end
 
   private
 
-  # Returns the events relation to use when JOIN LATERAL is not supported.
-  #
-  # This relation simply gets all the events for all authorized projects, then
-  # limits that set.
-  def relation_without_join_lateral
-    events = filtered_events.in_projects(projects)
+  def project_and_group_events
+    project_events = relation_with_join_lateral('project_id', projects)
+    group_events = relation_with_join_lateral('group_id', groups)
 
-    paginate_events(events)
+    Event.from_union([project_events, group_events]).recent
   end
 
-  # Returns the events relation to use when JOIN LATERAL is supported.
-  #
   # This relation is built using JOIN LATERAL, producing faster queries than a
   # regular LIMIT + OFFSET approach.
-  def relation_with_join_lateral
-    projects_for_lateral = projects.select(:id).to_sql
+  def relation_with_join_lateral(parent_column, parents)
+    parents_for_lateral = parents.select(:id).to_sql
 
     lateral = filtered_events
       .limit(limit_for_join_lateral)
-      .where('events.project_id = projects_for_lateral.id')
+      .where("events.#{parent_column} = parents_for_lateral.id") # rubocop:disable GitlabSecurity/SqlInjection
       .to_sql
 
     # The outer query does not need to re-apply the filters since the JOIN
     # LATERAL body already takes care of this.
-    outer = base_relation
-      .from("(#{projects_for_lateral}) projects_for_lateral")
+    base_relation
+      .from("(#{parents_for_lateral}) parents_for_lateral")
       .joins("JOIN LATERAL (#{lateral}) AS #{Event.table_name} ON true")
-
-    paginate_events(outer)
   end
 
   def filtered_events
@@ -97,4 +94,10 @@ class EventCollection
   def projects
     @projects.except(:order)
   end
+
+  def groups
+    strong_memoize(:groups) do
+      groups.except(:order) if @groups
+    end
+  end
 end